Berlin is located between the two major river basins of the Elbe and the Oder. The Spree and the Havel are the most important natural watercourses in the Berlin area. Additional natural watercourses include the Dahme, Fredersdorf Creek, the Straussberg Mill Stream, the Neuenhagen Mill Stream, the Wuhle, the Panke and Tegel Creek. Besides these natural bodies of water, there are a number of artificial bodies of water within the municipal area of Berlin, the canals. These include prominently the Teltow Canal, the Landwehr Canal and the Berlin Shipping Canal, with the Hohenzollern Canal.
The Spree is of special significance for the quality condition of Berlin streams. The canals in Berlin are predominantly fed by Spree water, so that their quality is influenced by the quality of that water. Since its effluent quantities are considerably higher than those in the upper Havel, the condition of the Spree water also decisively affects the quality of the Havel below the mouth of the Spree. In turn, the water condition of the Spree in the city is determined by numerous smaller tributaries within the municipal area.
Among Germany’s rivers, the Spree ranks only in the lower medium range. In comparison with the Oder (long-term mean flow at Hohensaaten-Finow: 543 cu.m./sec.) or the Elbe (long-term mean flow at Barby: 558 cu.m./sec.), the Spree and Havel, even when combined in the lower Havel, have only about one tenth the flow.
A quality measurement network is operated to monitor the quality of Berlin’s surface bodies of water; it concentrates as a matter of priority on ascertaining the impact of the numerous point-sources and diffuse water pollution sources along the course of the river. The measurement network includes a total of 63 measurement points, with 39 on the Dahme, Spree, Havel and the canals, and 24 on the smaller streams and lakes. As a rule, physical chemical, bacteriological and biological parameters are ascertained from monthly sampling tests.
For the continuous monitoring of oxygen conditions, the water temperature, the pH value and the conductivity, nine water quality measurement stations are also operated on the major streams.
As a rule, an average of 11 to 17 measurements are carried out per year at the sample measurement points. As a rule the 90th percentile (minimum sample size: n = 11) range is used to determine the quality classes. For the assessment of the temperature, the maximum value is used, and for the oxygen assessment, the minimum value.
At the continuously operating measurement stations, fifteen-minute values are ascertained and compiled to statistical key values. For the assessment of the temperature, the 95th percentile, and for the oxygen content the 10th percentile of day values are used. These values are of course more significant than the sample test results.