El Dorado ? Zebra mussels have returned in force to the El Dorado Reservoir this summer.

Craig Johnson, a state fisheries biologist for the lake, says summer testing found 114 zebra mussel larvae per liter of lake water. Last year, the figure was 4.5 per liter.

The Wichita Eagle reported Friday that the increase comes after three years of declines in zebra mussels at the reservoir.

El Dorado was the first lake in Kansas infested with zebra mussels in 2003. The population peaked in 2006 before beginning to decline in 2007.

Johnson said the population might have increased because almost no water was released from the reservoir this year.

Zebra mussels clog intake structures at power and water plants and can crowd out native species.