Seldom is clean water an issue for fish. But it is for fishermen at Lake Constance, or Bodensee in German. They claim the lake’s highly clean water lacks sufficient nutrients for fish to flourish, resulting in ever lower catches and dwindling profits.
“For years, nobody cared about environmental protection, but now the issue is exaggerated,” said Andreas Meichle, a Lake Constance fisherman whose family has been in the local fishing business for 14 generations. “They (environmentalists and politicians) haven’t been able to find a healthy balance.”
Lake Constance’s shoreline extends along the southwestern border of Germany and the northern borders of Switzerland and Austria. All three countries take great pride in the lake’s clean water quality and beautiful shores. The lake is a popular vacation destination and also an important source of drinking water.
But clean water is typically poor in nutrients, especially phosphate, a vital ingredient for the growth of algae and other plantlike organisms. These organisms, in turn, are essential for zooplankton, an important source of food for the lake’s famous whitefish.
“The lower the level of phosphate in the water, the smaller the whitefish population,” said Alexander Brinker, a limnologist and an expert on fresh water science.
Historically, fishing was not a major source of income for people living around Lake Constance. The lake had a naturally clear composition, which was poor in nutrients and high in calcium, and consequently lacked large populations of any kind of fish, not just whitefish.
But in the 1970s, Lake Constance underwent a phase of pollution, caused by fertilizers from nearby farms and other harmful pollutants that seeped into the lake. Algae thrived and thanks to higher amounts of phosphate in the water, fish populations grew. But at one point, the poor water quality also began to cause many fish to die.
Regional environmentalists and lake researchers reacted with demands for expanding German sewage facilities on the lake. State and federal policymakers in Germany approved the expansion, leading to today’s high level of clean water.
And that is a concern for Lake Constance fishermen, such as Mr. Meichle. “There is no way we can breed fish in mineral water,” he said. Revenue from fishing accounts for only 5 percent of his business these days – he makes most of his money from processing seawater fish from third parties and selling it.
Opinions vary on the state of fishing at Lake Constance and the action to be taken. “It is not a solution to manipulate the water for one group’s interest only,” said Herbert Löffler, a biologist with the institute for lake research at Lake Constance. Mr. Löffler sees no connection between the current condition of clean water and a lack in fish, noting that historically, there have been good and bad years in fish catches.
Yet the numbers indicate a severely declining population. In 2004, fishermen caught more than 800 tons of fish, compared to just 294 tons in 2013.
Experts are exploring alternative solutions to the problem, such as aquaculture facilities, where whitefish live in an artificial pool and are given powdered animal fodder, vaccinations and medication if needed. This form of breeding, however, is currently banned in Germany.