Until recently a lake in Berlin had been suffering an unwanted algae bloom due to an increasing phosphate concentration. The 700m x 100m Lake Plötzensee is popular with bathers and also for fishing and other forms of recreation and it was important that any method used to solve the problem didn't interfere with the natural ecosystem of the lake.

 A filter plant has now been added to the lake which includes sand filters and a filter containing 9m3 of Rowaphos. The water flow to the filter is 100m3 per hour, so the total volume of the lake is filtered 3-4 times a year.

Tests have found that this method has greatly reduced the phosphate levels while the depth of visibility in the lake is increasing. The bathers are happier too...