Massive fish kill on the Ypres-Yzer Canal: green thanks to duckweed
The phenomenon returns every year. The City of Ypres has declared the Vlaamse Waterweg in default and is demanding a definitive solution.
Oxygen deficiency
“For several years now, the Ypres-IJzer canal has been struggling with a problem of aggressive duckweed blooms,” said the spokesman for the City of Ypres.
“This plant covers the entire water surface in no time. It causes problems for the vessels, but also has an adverse effect on water quality. The oxygen levels drop to zero, causing all aquatic life to die. The thick silt layer in the Ypres marina, in combination with the persistent drought and increased water temperature, also causes a total lack of oxygen.”
Additional measures
The city of Ypres, as well as the Flemish Environment Agency and the Agency for Nature and Forests, have long been requesting parties to have the Vlaamse Waterweg, manager of the canal, take extra measures. This has been discussed several times.
“What had been feared for a while unfortunately turned out to be the truth on 1 August: there was a significant fish mortality among the duckweed. In combination with the high temperature, this creates an unpleasant odor,” says the City of Ypres.
A few weeks ago, the Vlaamse Waterweg did clear up part of the duckweed, but this was insufficient to contain the growth of the duckweed. From mid-July, the city insisted on doing this again as soon as possible on the top of the canal. Only after reporting the fish mortality did the city receive confirmation that the culling would begin soon.
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Mass fish kill: “Death channel”
“In recent years, the provincial fisheries commission has released fish in the canal and placed protective nets against cormorant predation,” said the spokesman for the City of Ypres.
“The anglers are now saddened to see how these efforts are proving to be in vain. The once beautiful fishing water is now a dead channel. The city therefore understands the dissatisfaction among anglers. Just as there is a lot of understanding for the unfortunate boatmen who get stuck in the thick pack of duckweed, for the tourists who no longer want to visit the Ypres harbor because of this, for the landlords who see their customers leave early and for the disgruntled local residents who look out on the green gunk and the odor nuisance.”
Aerators not enough
Just like in previous years, the city itself placed a few aerators in the canal as a precaution. This locally improves quality, but is of course just a drop on a hot plate. Since the spring of 2022, the VMM has been closely monitoring the water quality with multiparameter probes.
The oxygen values remain very low and already gave a signal that further action was necessary.
“Please dredge sludge urgently”
“Given that this happened insufficiently and late, the city has decided to declare the Vlaamse Waterweg in default”, says the City of Ypres.
“Although the city realizes that a solution is not easy and that the current weather conditions exacerbate the problem, the city believes that the agreements made earlier are not being complied with or insufficiently.
We request an accelerated approach. In concrete terms, this means that the Flemish Waterway must clear the sludge layer within the shortest possible time and that the duckweed approach must be accelerated and proactive”.