Zwarte Meer

The food chain of the Zwarte Meer

The Zwarte Meer is full of water plants, mostly under water. One plant stands out in the samples: the fringed water-lily. It has floating, almost round leaves and, in summer, yellow flowers above the water. It is not rare in the Netherlands, but you seldom find it in plant samples from other lakes. Here it was in 91 of 1,283 plant samples from 2005 to 2012. In comparable samples from other freshwater lakes you would expect it in about one of those 1,283.

The fish of plant-rich water stand out too. Tench live in shallow water with plenty of plants. The spined loach finds its food in fine sand and lays its eggs among plants. In trawl surveys in 2008 and 2011, tench were in 7 of the 16 catches and spined loach in 13. In comparable surveys of other freshwater lakes you would expect tench in fewer than one of the 16 catches, and spined loach in one.

Tench and zander both live here, and that stands out. Tench are fish of shallow water with plenty of plants. Zander are fish of large, murky water. In fish surveys of other freshwater lakes the two are caught together less often than you would expect by chance. Here both were in 6 of the 16 catches. We think the lake gives each of them a place: shallow water full of plants, and the deep shipping channels. We have not measured that. That is why there are two food chains below: one through the tench and one through the ruffe.

The water plants of the Zwarte Meer

The water of the Zwarte Meer has not always been this clear. Soon after the lake formed, in the 1940s, it held six kinds of pondweed and wide meadows of stoneworts, large algae that look like water plants. Too many nutrients in the water made the stoneworts disappear in the late 1950s. A few years later most of the pondweeds were gone too. The zebra mussels were also gone for a long time. They came back in the first half of the 1990s. They filter the water, and so it became clearer again. After 2008 stoneworts became more and more common, and now they rule under water. An evaluation from 2025 for Rijkswaterstaat, the Dutch national water authority, gives no explanation for that growth. The water stayed just as clear between 2010 and 2023.

Newcomers on the bottom

Four small water animals were not yet in the samples in 1993 and 1997. Three of them turned up from 2001: the Asian clam, a mysid shrimp (Limnomysis benedeni) and a bristle worm (Hypania invalida). The fourth, a tiny crustacean related to the woodlouse (Jaera istri), was first found in 2005. After that, all four were in more than half of the samples. The Asian clam comes from Southeast Asia. Of all new species of small water animals in the Rhine, the largest group comes from the region around the Black Sea and the Caspian Sea. Their spread grew sharply after the Main-Danube Canal opened in 1992.

You see the same among the fish. The tubenose goby, a small goby from the Black Sea region, was in 9 of the 16 trawl catches. In comparable surveys of other freshwater lakes you would expect it in fewer than one of the 16. In 2011 the monkey goby was in the net too, two years after the first confirmed find in the Netherlands.

Origin and history

Before the Zwarte Meer existed, this was the delta of the IJssel and the Vecht. Club-rushes grew naturally only around the mouth of the Zwarte Water. People in the region grew club-rushes and wove mats from them. When an offshore wind left the shallows dry, the town crier of Genemuiden called up day labourers, who then planted club-rushes. In the end the whole area between Vollenhove and Kampen was planted with them. Remains of those club-rush fields are still there. Club-rushes belong to the sedge family. In the plant samples from 2005 to 2012, plants of this family were almost three times as common as in comparable samples from other freshwater lakes. Here they were almost always club-rushes.

Fishing the Zwarte Meer

Always check the VISplanner, Sportvisunie’s map of Dutch fishing waters, to see whether and where you may fish on the Zwarte Meer.

The trawl surveys of 2008 and 2011 caught bream, ruffe, perch, roach, zander and eel, among others. According to the evaluation for Rijkswaterstaat, the fish surveys now mainly catch two non-native gobies: the round goby and the bighead goby, also called Kessler’s goby.

Notable species

The Zwarte Meer is a Natura 2000 site, partly for three fish that live on the bottom: the spined loach, the weatherfish and the bullhead. In 2022 the bitterling was added to that list. The bullhead has not been found in the lake since 2011. The evaluation for Rijkswaterstaat names the round goby and the bighead goby as one possible cause. Round gobies and bighead gobies push the bullhead out of its place on the bottom.