The State Environmental Service (VVD) draws attention to the fact that in places where thick ice and snow cover have formed on Latvian water bodies, fish suffocation may be observed as warmer weather begins. Fish suffocation is usually observed in February and March; to prevent this, it is recommended to create ice holes or, in smaller water bodies such as ponds, to perform water aeration by enriching them with air. Specialists recommend carrying out aeration in good time, preferably as early as January, before suffocating or dead fish are observed.
Fish suffer most from oxygen starvation in shallow and overgrown water bodies with slow water exchange, where the decomposition of aquatic plants consumes the oxygen present in the water. Under the ice and snow cover, water replenishment does not take place, and the intake of oxygen from the atmosphere has ceased. The only oxygen reserves in a lake or pond are those that accumulated before the ice cover formed.
Fish die in water with an insufficient concentration of oxygen. Most sensitive to reduced oxygen levels are salmonids – whitefish and vendace – as well as predatory fish such as zander and pike. Oxygen-starved fish concentrate near ice holes, especially pike and perch, where they can be easily caught by poachers. The VVD warns that such fishing is illegal.