Aquatic plants are only good in moderation. Too many nutrients and algae get out of hand, dramatically depleting oxygen levels. This is bad news for fish, for example, who then struggle to breathe or can’t breathe at all.
Berlin’s rivers, canals and lakes flow rather sluggishly. Water sticks around for an average of 59 days in the Großer Müggelsee and up to 183 days in the Tegeler See. These are ideal conditions for aquatic plants to flourish, which is less ideal. Permanent measuring stations and temporary measuring points across the city regularly determine how much chlorophyll, phosphorus or algae are present in the water. The visibility depth is measured, too.
The scale of water quality classes ranges from I to IV. Up until 2001, waters under scrutiny in Berlin were assigned the medium quality classes II-III and III. It was only the Tegeler See that received a class II ranking, which is the goal. Since the 1980s, the inflow from the north-east has been passing through a water treatment facility, filtering out phosphates. The Tegeler See is therefore living proof that the biological water quality can be improved by targeted measures.
Discover here how quality classes are established and what factors they are based on.