Mass fish mortality in the Noorderzijlvest region

1 July 2026, 15:06

There are currently several locations in the entire Noorderzijlvest Water Authority area where large-scale fish mortality has been observed. This applies to watercourses in rural areas and ponds in urban areas. Oxygen depletion caused by the severe weather last weekend, combined with the high temperatures of the past week, has led to this mass mortality. The water authority is working with external parties to remove the dead fish.

Severe weather is a major cause

Last weekend, severe storms passed through the Noorderzijlvest Water Authority region. The large amount of rainfall in a short period of time caused many sewer overflows. This led to a decrease in oxygen levels in ponds, canals, ditches, and lakes. Combined with last week’s high temperatures and the extent of vegetation growth in a number of watercourses, this has led to oxygen levels in the water falling too low, resulting in significant fish mortality.

Fish mortality is decreasing

With the current lower temperatures and the inflow of oxygen-rich water from the major watercourses in our water system, oxygen levels in smaller bodies of water and in the polders will rise. This will lead to a decrease in fish mortality.

Removing the fish

At the moment, the water authority is working with external parties to remove the dead fish. This work is expected to take a few more days. If you notice areas with a large number of dead fish, the water authority asks that you do not remove the dead fish yourself, but contact the water authority at 050-3048911. The water authority is monitoring the situation.

Previous report of dead fish in Hoornsegraft

Last Saturday 27 June, we received a report of a large number of dead fish in the Hoornsegraft in Groningen. An enforcement officer visited the site and measured the oxygen level in the water. These measurements showed that the oxygen level was normal. The water quality and flow were also checked. The deeper part of the watercourse was also clean and clear. The dead fish were removed last Monday.