OXFORD PUBLIC (INTERNATIONAL LAW
Max Planck Encyclopedia o f Public International Law
Estuaries
Erik Franckx
Content type:
Product: Max Planck
E ncyclo p e d ia E ntries
E ncyclo p e d ia o f Public
In te rn a tio n a l Law [MPEPIL]
A rticle last updated: June
2007
Subject(s):
Pollution — Bays — UNCLOS (UN Convention on the Law o f the Sea) — Delim itation — Marine
environm ent, p ro te ctio n — Rivers
Published under the auspices o f the Max Planck Institute fo r C om parative Public Law and International
Law under the d ire ction o f R udiger W olfrum.
From: Oxford Public International Law ( http://opil.ouplaw.com). (c) Oxford University Press, 2013. A ll Rights Reserved. Subscriber: G ent University; date:
17 June 2014
A. N otion
1 Although w ell-established in scientific literature, the m eaning o f the term ' e s tu a ry ' has
attracted only lim ited consideration in international law. Scientific literature has defined it as
'denoting a sem i-enclosed coastal body o f w ater which has a free connection with the open sea
and within which sea w ater is m easurably diluted with fresh w ater derived from land drainage'
(Cam eron and Pritchard). A glossary drawn up to assist the understanding o f the 1982 United
Nations Convention on the Law o f the Sea ('UN Convention on the Law o f the Sea') defines the term
as follows: 'The tidal m outh o f a river, where the seaw ater is m easurably diluted by the fresh w ater
from the river' (A Manual on Technical Aspects o f the United Nations Convention on the Law o f the
Sea A ppendix I: Glossary, para. 32; see also Law o f the Sea).
2 Salinity form s the basis o f a w ell-established definition o f an e s tu a ry used by m o st estuarine
scientists. A ccording to accepted practice in the scientific co m m u n ity, in this transitional area, any
waters with a salinity level o f between 5 and 34 parts per thousand are generally considered to be
estuarine. A nother criterion is found in the topography test, based on features relating to the
ch a ra c te r o f the waters, such as tidal m o ve m e nts and sedim ents. E stu aries are often known as
bays, lagoons, harbours, inlets, or sounds (Bays and Gulfs). However, not all w ater bodies
addressed by those nam es are necessarily e s tu a rie s .
B.
Estuaries in the Legal Sphere
3 In the legal sphere, the term surfaced during the preparations o f The Hague Codification
Conference o f 1930 (see also Law o f the Sea, History of). Since several countries had indicated
the ir desire th a t rivers flowing d irectly into the sea w ithout an e s tu a ry should be considered
inland waters, irrespective o f the ir breadth, this was included in the Basis o f Discussion a t 18, to
which the following sentence was added: 'If a rive r flows into an e s t u a r y , the rules applicable to
bays apply to the e s tu a r y '. This provision, restricted to single State e s tu a rie s , found its way into
the report o f Sub-C om m ittee II o f the Second C om m ittee and was taken up by rapporteur JPA
François in his preparation fo r the 1958 Convention on the Territorial Sea and the Contiguous Zone
(see also C onferences on the Law o f the Sea; Territorial Sea; Contiguous Zone). In a co m m e n t, the
International Law Com m ission (ILC) expressed its uncertainty since it lacked sufficient
geographical data to appreciate the im p a ct o f this provision on all e s tu a rie s and one country
had particularly raised the specific issue o f the River Plate. During the co nference itself, the United
States o f A m erica ('US') pointed a t the lack o f a precise legal o r geographical m eaning o f the term
' e s tu a r y ' and argued th a t reference to the c o n ce p t o f bays was superfluous because the latter
would apply anyw ay if a particular e s tu a ry fulfilled the requirem ents o f a juridical bay. The
provision passed the First C om m ittee, but not the plenary session, where it was defeated. It is
nevertheless interesting to point o u t the difference which exists in this re sp ect between the English
te x t on the one hand, and the French on the other, fo r the latter has retained the term in the first
paragraph o f Art. 13: 'If a rive r flows d irectly into the sea' corresponds with ' [s]i un fleuve se jette
dans la m e r sans fo rm e r d 'e stu a ire '. The Russian and the Spanish authentic texts rather follow the
English structure.
4 A gainst this background, the rule has developed th a t when rivers form an e s t u a r y , their
baselines are determ ined under the provisions relating to jurid ica l bays. This was co nfirm e d by
national c o u rt decisions, first by the US Suprem e Court in the United States v California Cases,
where the Court stated in early 1966 th a t '[a ]n e s tu a ry o f a rive r is treated in the sam e way as a
b ay' (U nited S tates v C alifornia [S up p lem en tal D ecree] para. 4 (d)), and a few m onths later by
British courts having to decide w hether broadcasting activities from a structure in the Tham es
e s tu a ry about 5 nautical miles ('n m ') from the nearest coast, fell under the 3nm jurisdiction
claim ed a tth a ttim e by the United K ingdom .The British c o u rt finally held th a t these activities had
taken place in internal waters, thus accepting th a t the Tham es e s tu a ry could be closed o ff by a
closing line since it constituted a juridical bay. It should nevertheless be noted th a t by m aking use
o f the c o n c e p t o f ju rid ica l bays, the latter's im perfections are also taken o v e r such as the
unanswered question o f how to tre a t e s tu a rie s the coasts o f which belong to two or m ore States.
From: Oxford Public International Law ( http://opil.ouplaw.com). (c) Oxford University Press, 2013. A ll Rights Reserved. Subscriber: G ent University; date:
17 June 2014
5 The term resurfaced during the preparations fo r the UN Convention on the Law o f the Sea, but in
two d ifferent spheres, nam ely anadrom ous fish species on the one hand and pollution, especially
land-based pollution, on the other. Only Romania tried to follow up on, and even furthe r develop,
the legal discussions o f the term during previous codification attem pts by subm itting d ra ft articles
on delim itation o f which the ve ry last sentence read: 'The term inal point o f a rive r fro ntie r shall be
considered as the im m ediate confluence o f the rive r and the sea, irrespective o f w hether the river
flows into the sea in the form o f an e s t u a r y ' ('R om ania: D raft Articles on Delim itation o f Marine
and Ocean Space' Third United Nations Conference on the Law o f the Sea [23 July 1974] UN Doc
A/CONF.62/C.2/L.18). This proposal did not m e e t with success, fo r the 1982 Convention on the Law
o f the Sea, e x c e p t fo r the French version o f Art. 9 th a t was taken o v e r from the 1958 Convention on
the Territorial Sea and the Contiguous Zone as explained above, only refers to e s tu a rie s in two
particular instances. First, when defining 'pollution o f the m arine e n viro n m e n t' as m eaning 'the
introduction by m a n ...o f substances or energy into the m arine environm ent, including e s tu a rie s '
(Art. 1 (4) UN Convention on the Law o f the Sea), and second, when providing th a t States are
required to adopt laws and regulations and o ther necessary m easures to prevent, reduce, and
control pollution from land-based sources, including rivers and e s tu a rie s (ibid Art. 207 (1) and
(2)). The reference to e s tu a rie s with re sp ect to the life cy c le o f salm on only m ade it into a
working paper o f the Second C om m ittee. Since States are to a c t in particular through co m p e te n t
international organizations o r a diplom atic co nference in order to e n d e avo u r to establish global
and regional rules, standards and re co m m e nd e d practices with re sp ect to land-based pollution, the
notion ' e s tu a ry ' is often encountered in international e nvironm ental instrum ents, such as the
1992 Convention on the Protection o f the Black Sea against Pollution o r the 1995 Global Program m e
o f Action fo r the Protection o f the Marine E nvironm ent from Land-Based A ctivities. The term also
figures in EC law, eg D irective 92/43/EEC on the C onservation o f Natural Habitats and o f Wild Fauna
and Flora ('Habitats D irective'). But in none o f these instrum ents is the term ' e s t u a r y ' defined.
C.
Estuaries in the European C o n text
6 In the European context, the question o f the m eaning o f the term ' e s t u a r y ' arose in 1996
before the English High Court, which, fo r the first tim e, provides guidance as to the judicial
characteristics o f an e s t u a r y . A t the heart o f the dispute was the c o rre c t way o f establishing the
o uter lim it o f an e s tu a ry in accorda n ce with the definitions o f ' e s tu a ry ' and 'coastal w aters' in
EEC D irective 91/271 concerning Urban W aste W ater T reatm ent. The conditions fo r certain w ater
discharges were m uch m ore restrictive, and thus costly, in e s tu a rie s than in coastal waters. For
the purpose o f this D irective, M em ber States o f the European (E conom ic) C om m unity (EC) are
required to establish the o ute r seaward lim its o f e s tu a rie s . It defines ' e s tu a rie s ', as to the
nature o f the receiving waters, as 'the transitional area a t the m outh o f a river between fresh w ater
and coastal w aters' (Art. 2 (12) D irective 91/271). 'Coastal w aters' are defined as 'the waters
outside the low-w ater line o r the o ute r lim it o f an e s t u a r y ' (Art. 2 (13) D irective 91/271). No
definition o f 'fresh w ater' is provided, nor is there any specification on which criteria to apply when
establishing an outer estuarine limit. In this case, the defendant took the view th a t in addition to
salinity or topography, the co st o f tre a tm e n t o f the waste w ater could also be considered when
determ ining w hat constitutes an e s t u a r y . For th a t reason, the S ecretary o f State had chosen two
bridges o v e r the H um ber and the Severn e s tu a rie s as the ir outer boundaries in the fra m e w o rk o f
this D irective—fo r the fo rm e r this is about 43km furthe r inland— allowing the m unicipalities to
discharge waste w ater beyond this point w ithout having to co m p ly with the m ore stringent and
expensive requirem ents o f secondary treatm ent. The judge did not interpret the D irective as
confining the M em ber States to the criteria o f salinity o r topography when establishing outer
estuarine limits. These were not the only re le van t considerations which could be taken into
a c c o u n t when m aking a 'genuine and rational a ssessm en t...o f w hat actually constitutes an
e s tu a ry ' (R v S ecreta ry o f S tate fo r the E nvironm ent, e x p a rte Kingston upon H u ll C ity Council
and R v S ecretary o f S tate fo r the E nvironm ent, ex p a rte B ris to l C ity Council and W oodspring
D is tric t C ouncil 344). However, the c o s t o f tre a tm e n t o f waste w ater was not a relevant
consideration in th a t exercise. The English High Court seem s to have been guided by a teleological
interpretation since the D irective distinguished between e s tu a rie s and coastal waters e xactly
because the latter have a better ca pa city to assim ilate the discharge o f waste water.
From: Oxford Public International Law ( http://opil.ouplaw.com). (c) Oxford University Press, 2013. A ll Rights Reserved. Subscriber: G ent University; date:
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7 Moreover, the d ire ctive's pream ble referred to a 1988 EEC Council Resolution adopted pursuant
to the 1987 Second International Conference on the Protection o f the North Sea. The Ministerial
Declaration o f th a t co nference supported the distinction between e s tu a rie s and coastal waters in
taking precautionary action to p ro te ct the m arine environm ent. The principal convention on which
such m easures are based was the 1974 Paris Convention fo r the Prevention o f Marine Pollution
from Land-Based Sources ('Marine Pollution C onvention'). The latter defined the 'm a ritim e area' for
establishing the geographical co verag e o f the convention, as extending in the case of
w atercourses up to the 'freshw ater lim it', which is defined as 'the place in the w atercourse where,
a t low tide and in a period o f low freshw ater flow, there is an appreciable increase in salinity due to
the presence o f seaw ater' (Art. 3 Marine Pollution Convention). Identical form ulations were found in
a num be r o f subsequent agreem ents on land-based sources o f m arine pollution, recognizing
salinity as a relevant criterion in differentiating between these separate bodies o f water.
D.
Estuaries and Intern ation al W atercourses
8 The term has also found a new field o f expansion in the area o f the law o f international
watercourses. Since the adoption o f the 1997 Convention on the Law o f Non-Navigational Uses of
International W atercourses, where in Art. 23 on the protection and preservation o f the m arine
e n v iro n m e n t e s tu a rie s are e xplicitly included, this has served as an exam ple fo r oth e r regional
agreem ents, eg in Art. 4 (2) (d) o f the 2000 Revised Protocol on Shared W atercourses in the
Southern A frican D e velopm ent C om m unity (SADC), and the co ncrete rive r basin agreem ents
concluded under its auspices, eg the 2002 Interim A gre e m e n t fo r Co-operation on the Protection
and Sustainable Utilisation o f the W ater Resources o f the Incom ati and Maputo W atercourses,
between M ozam bique, South Africa and Swaziland, where the e s tu a rie s are not only included in
the definition o f these rivers, but where in cases o f drought, the estuarine ecosyste m s will only
suffer in the last resort as specifically provided in Annex I Arts 4 (5) [Inco m a ti] and 6 (5) [Maputo].
Much scientific research has already been done as to the e ffe ct o f w ater use upstream and dam
building on the dow nstream estuarine ecosystem o f the Incom ati, fo r instance, suggesting tha t
e s tu a rie s o f rivers, and the ir e cosystem s, should receive a m ore pro m in en t role in the quest o f
the parties to arrive at an equitable and reasonable utilization o f the w ater resources, as provided
in Art. 3 (b) o f the latter a g ree m e n t (Equitable Utilization o f Shared Resources).
E. Conclusion
9 The conclusion therefore seem s to be justified th a t e s t u a r ie s — which by the ir ve ry nature
belong as m uch to the freshw ater regim e as to the seaw ater regim e— have in law fo r a long tim e
been treated in a stepm otherly fashion by freshw ater law as well as the law o f the sea, being
located a t the outskirts o f both disciplines. A t present, only a scientific definition o f the term
' e s tu a r y ' exists at the international level, not a legal one, even though m ore and m ore legal
d ocum ents appear to m ake use o f it.
S elect Bibliography
DW Pritchard 'Estuarine H ydrography' (1952) 1 A dvances in G eophysics 243-80. Find it in
y o u r Library
WN C am eron and DW Pritchard ' E stu aries ', in MN Hill (ed), The Sea (W iley New York 1963)
vol 2, The C om position o f S ea-W ater C om parative a nd D e scrip tive O ceanography. Find it in
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ED Brown 'D elim itation o f Maritime Frontiers: Radio Stations in the Tham es E s tu a ry ' (1966)
2 AustYBIL 99-113. Find it in y o u r Library
RSK Barnes and J Green (eds) The E stuarine E n viro n m e n t (Applied Science Publishers
Barking 1972). Find it in y o u r Library
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A griculture O rganization o f the United Nations Rome 1990). Find it in y o u r Library
C Blatch ' E stu aries and Coastal W aters— Establishing the Limits: R v S ecreta ry o f S tate fo r
the E n v iro n m e n t e x p a rte K ingston-U pon-H ull C ity C ouncil and R v S ecreta ry o f S tate for
From: Oxford Public International Law ( http://opil.ouplaw.com). (c) Oxford University Press, 2013. A ll Rights Reserved. Subscriber: G ent University; date:
17 June 2014
the E n v iro n m e n t e x p a rte B ris to l C ity C ouncil and W oodspring D is tric t C o u n cil’ (1996) 8
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S elect Docum ents
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and opened fo r signature 21 May 1997, not y e t entered into force) (1997) 36 ILM 700.
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[1991] OJ L135/40.
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Wild Fauna and Flora [1992] OJ L206/7.
E stu ary Restoration A c t (7 N ovem ber 2000) (2000) 33 USC para 2901-09.
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v S ecretary o f S tate fo r the E nvironm ent, ex p a rte B ris to l C ity Council and W oodspring
D is tric t C ouncil UK Queen's Bench Division (26 January 1996) [1996] E nvironm ental Law
Reports 248. Find it in y o u r Library
'Rom ania: D raft A rticles on Delim itation o f Marine and Ocean Space between A djace n t and
Opposite Neighbouring States and Various Aspects Involved' Third United Nations
Conference on the Law o f the Sea (23 July 1974) UN Doc A/CONF.62/C.2/L.18.
Tripartite Interim A gree m e n t between the Republic o f M ozam bique and the Republic o f South
Africa and the Kingdom o f Swaziland fo r Co-operation on the Protection and Sustainable
Utilisation o f the W ater Resources o f the Incom ati and Maputo W atercourses (signed 29
A ugust 2002)
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into force 16 N ovem ber 1994) 1833 UNTS 3.
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the Marine E nvironm ent from Land-Based A ctivities' (5 D e ce m be r 1995) UN Doc
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DC 31 January 1966) (1966) 5 ILM 205.
From: Oxford Public International Law ( http://opil.ouplaw.com). (c) Oxford University Press, 2013. A ll Rights Reserved. Subscriber: G ent University; date:
17 June 2014