Prevent fish mortality | craft.net

September 05, 2022 • 10:57

DRECTHSTEDEN – Water Naturally makes an urgent appeal to managers of waterways. Avoid unnecessary fish kills due to unwise management. Warm weather makes for warmer water. The result is less oxygen. Fish can then have a hard time resulting in death. Leave the water alone as much as possible during this warm time.

fish mortality

The water manager cleaned a ditch near Puttershoek last week. Aquatic plants were mowed and set aside. That is necessary periodically. Waterways have a natural tendency to grow dense and with the large amount of fertilizers in the water this happens extra quickly. Blockage of the water system must be prevented to ensure the necessary supply and drainage of water.

However, the water system is more than a system for supplying and draining water. It is the habitat for fish and other aquatic life. They also play an important role in the natural processes that should keep the water clean and healthy. The water manager must – in the view of Water Naturally – take this into account. Cleaning locks in the current hot conditions is not wise.

That became apparent again last week. Fish mortality occurred as a result of the cleaning of a waterway. A passerby filmed the dying fish and reported it to Water Naturally. It is not yet known whether the Hollandse Delta water board or the municipality of Hoeksche Waard is responsible

Triple negative

The warmer the water, the less oxygen it can hold. Oxygen is crucial for aquatic life. Too little means suffocation and death. This is therefore an important point of attention for the water manager. They must know where the critical limit is and take it into account. At the end of the last century there were already plans for this at the water board, but they are still in a drawer.

Cleaning ditches means a significant attack on the oxygen content in the water during and after work. This is partly due to the stirring up of bottom sludge. As a result, the oxygen content can drop below the critical limit, resulting in dead fish.

Aquatic plants are removed from the ditch. They actually produce oxygen and thus help in this difficult time to maintain the oxygen level in the water. As a water manager, you put an abrupt end to this if you remove those plants.

The message from Water Of course is: maintenance is necessary, but think before you start and avoid fish deaths.

Joost Kievit MSc

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