At least that's what a group of anglers contend, blaming swimmers for the 500 dead fish that have turned up in a picturesque German lake near Hamburg, The Local reported.
"Swimmers who urinate in the lake are introducing a lot of phosphate," Manfred Siedler, a spokesman for an angler’s group, told Bild newspaper. "We're calculating half a liter of urine per swimmer per day."
Skeptics questioned whether the outcry was an attempt by fishermen to oust bathers – with whom they have long feuded, according to The Local – but are saying this could be possible.
IO9.com, a Gawker science blog posed the question, “Can anything as natural as peeing in a lake kill the fish?”
The answer, apparently, is yes.
The urine itself doesn’t harm the fish but sets off a series of environmental events that ultimately suffocate the fish.
First, the urine acts as a fertilizer for the blue-green algae in the water. Once they have consumed all the fertilizer, the algae continue sucking up available oxygen in the water, IO9.com explained. When the algae die and start to decompose, they further use up oxygen. That’s when fish start to die.
Bild reported that authorities have poured more than half a million dollars of an anti-phosphate agent called Bentophos into the lake, to no avail.
(Bentophos has been tested in artificial lakes that were shut down due to massive bacterial blooms.)
For now, the lake is closed to swimmers because of the high levels of algae (which can cause swimmer's itch), but the city's environmental authority is fighting the closure, The Local reported.
Kerstin Graupner, a spokeswoman for the environmental authority, told The Local that she blamed natural causes and ice-skaters.
"The ice-skaters make a noise that wakes the fish out of hibernation," Graupner said. "Then they can't breathe and freeze. That's a very common phenomenon."
Graupner’s agency called on a university in Hamburg to test the anglers’ theory. According to The Local, it appears the anglers may have a point – the scientists found anabaena algae blooms, which produce a toxin that ultimately restricts fish breathing.
The German lake isn’t the only place where officials worry about swimmers; signs at the Great Barrier Reef ask swimmers not to urinate in the water. Doing so apparently kills the corals, which grow in low nutrient waters.