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A view of the lagoon near Cap Malheureux
What is a Lagoon?
Stresses on the Lagoons
The island of Mauritius is surrounded in most parts by lagoons
created by the formation of either barrier reefs or fringing reefs.
The area of the lagoons is 243 square kilometres. They are vitally
important as sources of food through artisanal fishery, as places
of leisure for both the population and tourists. Unfortunately,
development and industrialisation are taking their toll, and dearly
Lagoons are areas of relatively shallow water situated in a coastal environment and having access to the sea but separated from the open marine conditions by a barrier. The barrier may consists of sandbars, barrier islands or coral reefs. There are two types of lagoons: (1) elongated or irregular stretches of water that lie between coastal barrier islands and the shore line known as coastal lagoons and (2) circular or irregular stretches of water surrounded by coral atoll reefs or protected by barrier coral reefs from direct wave action known as coral lagoons.
The second form of lagoons are restricted to tropical open seas
that provide the conditions necessary for coral growth.
In Mauritius, most lagoons are of the coral type, though a few lagoons exist which are of the second type. For example, along the western and south western coasts, coastal processes were at work in the formation of lagoons. Along those coasts, long shore currents move coastal sediments along the mouths of streams resulting in marshy lagoons. Such coastal lagoons can be seen at Wolmar, La Priairie, and Anse St Martin.
Human activities which have an impact on the lagoons are: hotel development, sand extraction, artisanal fisheries, operation of leisure boats, industrial sewage, domestic sewage and solid waste disposal. Please follow the hyper links for further information.
The Albion Fisheries Centre has carried out a number of measurements on the water quality on the lagoon at selected sites. Each site was visited 6 times over the course of a year.
The laboratory analyses consisted of the following measurements: Nitrate-Nitrogen, Phosphate and BOD5.
The normal values for the above are as follows:
Nitrate Nitrogen: 0.1 - 0.2 mg/l
Phosphate : 0.02 - 0.04 mg/l
BOD5 : 0 - 1.0 mg/l
For 1996, the average values (in mg/l) of the parameters analysed for the different sites are as follows:
|Ile Aux Benitiers||ND||0.014||0.38|
|Trou d'Eau Douce||ND||0.015||0.52|
|Anse La Raie||0.02||0.013||0.51|
|Trou Aux Biches||ND||0.014||0.52|
|Pointe Aux Sables||ND||0.022||1.09|
|Port Louis Harbour||ND||0.040||1.05|
Source: Ministry of Cooperatives, Fisheries and Marine Resource Development, Annual Report 1996
The centre at Albion also carried out bacteriological analyses
of sea water near Albion itself, they did report the presence
of coliform bacteria at the mouth of Belle Eau river that discharges
in the Albion Lagoon.
The annual report mentions a number of abnormal events that occurred
during 1996. Fish mortality was reported twice, once at Bain Des
Dames and once at Tombeau Bay, both localities being situated
close to Port Louis Harbour. Outpourings of sewage leading to
eutrophication and high BOD loads were thought responsible.
In the north, at Trou Aux Biches and Mon Choisy, several occurrences
of red tides were reported. The causes of theses red tides are
not known. In 1992 too, there were occurrences of red tides which
had caused massive fish mortality.
Last Update: Thursday, February 05, 1998