HAMBURG â€"  Swimmers have killed about 500 fish in a northern Germany lake, with their urine causing algae that poisons marine life.

The mass death in the past two weeks has occurred in Eichbaum lake, in the port city of Hamburg, The Local reported.

"Swimmers who urinate in the lake are introducing a lot of phosphate," fishermen's spokesman Manfred Siedler told Bild newspaper. "We're calculating half a liter [0.15 of a gallon] of urine per swimmer per day."

Applying anti-phosphate -- at a reported cost of $667,000 -- hasn't worked, fueling an ongoing feud between fishermen and those who swim in the lake.

Swimmers have been banned from the lake until the algae outbreak is addressed.