Tjeukemeer, a man-made lake, is located at a beeline distance of about 80 km northeast from Amsterdam, beyond Ijsselmeer. Like many other lakes in the Netherlands, this freshwater lake has been built on polder or the land reclaimed from the sea, where sandy soil prevails and the landscape is strangely deficient in vegetation. The lake has a mean depth of 1.8 m, a maximum depth of 5 m, and the water surface lies 1 m below sea level. The surface, however, covers 21 km2, displaying a great achievement in reclamation work which has gathered worldwide reputation.

The residence time of the lake water is fairly short (ca. 0.17 year) because of its shallow depth and small volume. Thermocline does not form throughout the year, and the lake may be frozen for two months during some winters. Transparency ranges from 0.5 m to 1.0 m, and the pH value is always above 8.0, often approaching 9.0. The phytoplankton biomass fluctuates from year to year, but tends to be elevated from May to September and may reach 400-500 mg l-1. Blue-green and green algae predominate the phytoplankton community; about 80% are blue-green from April to July and a similar dominance of green algae is observed from September to December. Eels are an important fishery product of this lake (Q).