Etyek Fishing Lake


The lake is situated in a valley just next to the city of Etyek. Its watershed is fairly big, and due to this fact the lake’s nutrient load is high due to municipal and agricultural related penetration of Nitrogen and Phosphorus compounds. Water exchange in the lake is minimal, in dry seasons there are completely no inlet and outlet. Before our treatment the dissolved oxygen balance of the lake was really bad, DO levels were quite low throughout the lake in every segment of the water column. This resulted moderate but continuous fish kills among those species that are very sensitive to the decrease of DO. The width of the bottom sludge layer is fairly high, the sludge is unstable and rotting, gas production is continuous everywhere at the bottom. Rotting sludge and bad DO conditions (anaerobic and anoxic) are the cause of the existence, and high concentration of dissolved rotting organic materials in the water. The nutrient content of these organic materials is not known, so this is an additive nutrient source for the algae.

The local fisher’s association that is the owner and the manager of the lake as well has searched us, and wanted to turn the eutrophic processes in reverse. In 16th June 2007 the bioremediation of the lake has started. The continuous fish kill has stopped in 2 days after the first treatment as the stabilization of DO started. The lake has escaped algae blooms during the summer, despite the total algae count was high at the start of the treatment, for the end of the summer a significant decrease in their number could be observed alongside with the decrease of nutrient concentrations in the water, and the improvement of water quality. Tables below are showing the most important water quality parameters and the changes in DO levels before and after the treatment.

Etyek Fishing Lake 19th June 2007. 01th October 2007.
Ammonium mg/l 0,31 0,28
Free Ammonia mg/l 0,01
Nitrite mg/l 0,08 0,07
Nitrate mg/l 18,4 13,2
Ortophosphate mg/l 0,34 0,2
Total Algae Count / ml 28 950 21 802

Etyek Fishing Lake
Oldott oxigén
16th June 2007.
1st treatment
29th June 2007.
2nd treatment
14th September 2007.
3rd treatment
top 3.64 mg/l 6.5 mg/l 10.82 mg/l
middle 3.11 mg/l 5.85 mg/l 10.63 mg/l
bottom 2.35 mg/l 5.82 mg/l 9.49 mg/l

A significant part of the microorganisms has settled to the bottom of the lake, and started the biodegradation of the organic sludge layer. The decrease of the thickness of the sludge was significant, as it is shown in the table below:

Date Height of sludge layer
2007. június 29 cm
2008. március 14 cm