Fish began floating to the surface of Sterling Lake on Tuesday in what has become a significant fish kill at this popular summer locale.



�They were pulling out humongous catfish; some were over 15 pounds,� Sterling resident Deb Oden said. Those fish were alive and taken to the river.



�The ducks are doing a nice job with cleanup,� Oden said.



While Oden saw many fish saved � such as bass, flatheads, perch, carp and shad � by the quick action of local residents, probably thousands died from what city officials described as an excessive growth of naturally occurring green algae.



�The water is not deemed to be dangerous and is not believed to be part of a group of other lakes in the state affected by blue-green algae,� said City Manager Taggart Wall. �Fish kills often result from natural events, particularly too little oxygen in the water.�



Officials from Sterling contacted the Kansas Department of Wildlife, Parks and Tourism, which helped them assess the situation.



Circumstances that can contribute to the fish kill include large amounts of decomposing organic material.



�This organic material can enter the lake from the surrounding street and yard drainage as well as through duck, goose and grass-eating carp excrement. The presence of this material interacts favorably with the plant life in the lake, raising the nutrient levels of the lake and subsequently creating an algae bloom,� Wall said.



While algae produces oxygen during the day, algae uses it at night or when the sun is not shining, lowering oxygen levels. During the nighttime and cloudy weather, low sunlight causes algae to switch from photosynthesis to respiration, consuming oxygen needed by fish. During severe events, fish can suffocate from low oxygen.



Wall said that algae in a lake is not a bad thing and much of the oxygen available to fish comes from algae. However, excessive algae becomes a problem. The city has been monitoring algae conditions at the lake all season and especially in preparation for Sterling�s Old Fashioned Fourth of July.



�We are mindful of the role the lake plays in the community,� Wall said. �The lake will recover through the introduction of oxygen.�



Wednesday, as dead fish continued to float near the shore of the lake, more oxygen was being introduced through small on-shore compressors connected to air diffusers at the bottom of the lake.



The aerators, Wall explained, are designed to move the low oxygen water at the bottom of the lake to the surface of the lake.



�This creates a vertical mixing pattern, which would otherwise not occur,� said Wall. �They add very little oxygen directly to the water; most oxygen uptake for the water takes place at the surface where the water interacts with the atmosphere. That�s why we need some wind to help move the water around and break up the algae coverage.�



George Lyster came to check out the condition of the lake and said he has seen this happen before. Wednesday morning he saw a skid loader filled with dead fish. There were probably hundreds of pounds of fish.



�The beach area was lined with dead fish,� Lyster said.



The city does not expect a complete kill, as those are very rare, Wall said.