Abstract:
Beira Lake is located in the heart of the city of Colombo.and in an highly
urbanized catchment of 432 ha. Beira Lake covers 65.4 ha and comprises four main
basins the East Lake, the Galle Face Lake, the West Lake and the South West Lake.
The objective of the study was to determine the trophic status of the lake using the,
physical, chemical and biological properties of the water.
The mean water transparency depth of the lake was 15.2±9.2 ern. The
euphotic zone was approximately 41.8 cm. Water temperature ranged from 26°C to
32°C. Conductivity ranged from 212 to 500 IlS. pH value ranged from 7.2 to 9.8
Dissolved Oxygen, BOD and Orthophosphate values of the lake ranged from 7.82
to 14.41 mg/I, 33.45 to 68.35 mg/1 andO.014 to 0.08 mg/l respectively. The highest
and lowest Sulphate values recorded were 4.04 ppm and 2.33 ppm. The Chloride
content ranged from 29.02 to 53.09 mg!.
The phytoplankton community of the Biera Lake composed of the dominant blue
green algae and the green algae. Blue green algae represented 99 percent ofthe total
phytoplankon population. The major zooplankton groups observed werecladocerans,
Copepods and Rofiters. Copepods were the most dominant zooplankton group.
According to the physical chemical and biological properties obtained for Beira
Lake, it is at the advanced stage of eutrophication process.
