Shrimp farming is rapidly expanding over a coastal belt of about 120 km in
the northwestern province of Sri Lanka. The Dutch Canal Mundel lagoon syste
m, a shallow semienclosed coastal water system with very limited tidal mixi
ng due to sandbar formation, act as the major brackish water source and a r
eceiving body for the effluents discharged for 70% of the shrimp farms in S
ri Lanka. Farms are mainly developed on intertidal areas in land-use catego
ries of mangroves, salt marsh and scrubland; occupying more than 60% of the
natural flood plains. Floods during intermonsoons have affected 40% of the
farms directly and retension of flood water in lagoons has resulted in unu
sually low salinities (2 ppt) for 2-5 weeks, restricting water exchange in
farms. Concentrations of sulfides (5.2-8.0 mg L-1) and nitrites (0.58-0.93
mg L-1) were at suboptimal levels in culture ponds during rainy seasons. Co
ntamination of water source by discharged effluents is evident due to unpla
nned location of inlet and outlet canals. Highly acidic water (pH 3.5) with
high concentrations of aluminum (1.8-2.5 mg L-1), manganese (0.16-3.6 mg L
-1) and iron (1.7-19.3 mg L-1) were observed in water discharged to the maj
or waterbodies from ponds built on acid-sulfate soils. Self-pollution cause
d by farming activities has resulted in environmental degradation which in
return has caused major problems to the shrimp farming industry. High incid
ence of disease symptoms, growth retardation, poor shrimp quality, socioeco
nomic problems together with environmental problems have caused major threa
ts to the industry. Better planning with due consideration to environmental
and socioeconomic problems when locating and constructing shrimp farms wou
ld help to improve and ensure sustainability of the industry.