With exaggeration it can be said that zebra mussel (lat. Dreissena polymorpha) that we will talk about, is only returning home. Before the last ice age, it has been abundantly found throughout Europe, but the gradual glaciation has pushed it into the areas of Azov and Caspian Seas. As the climate warmed, its expansion back to Europe began in the 19th century.
At the same time, however, the industrial revolution began, and so its move seemed to slow down. Since zebra mussel is extremely sensitive to pollution, which is used in the creation of biological warning systems, in which technical means register the response of the mussel to environmental pollution.
With improving water quality, warming climate and increasingly greater movement of people and means of transport between continents, the expansion of zebra mussel in the 1980s has advanced again.
Since then it has conquered Europe, except Norway, Iceland and Faroe Islands and has spread to the whole of North America. It is therefore no surprise that this species has been ranked among the 100 worst invasive animals in the world and is also in the list of the European Environmental Agency´s 163 most dangerous invasive species, threatening the original ecosystems in Europe.
Although the zebra mussel is only about 3 to 4 centimetres in size, it can cause a lot of trouble. In the beginning it seemed that during normal operation of hydro power stations the mussel did not interfere.
However, problems occurred during repairs or emergencies at hydro power stations. For example, several tons weighing falling gate when closing at the same time wiped off the shells and pushed them underneath. Accumulated shells then prevented the gate to reach the bottom threshold. The divers had to be called and their manual cleaning resulted in several days of delays with repairs.
The problems were very similar at all power stations in the middle and lower flow of the Vah river: the mussels covered a continuous surface of concrete structures from the gates to the turbine blades.
In addition, after the water was drained, they immediately died and rotting animals caused an unbearable odour causing nausea.
Despite the measures the mussel has penetrated further “inside“ the power station. The mussels have reached the turbine cooling system resulting in a reduced flow profile and thus also gradual reduction in the efficiency of coolers.
The literature describes many ways and methods of combating occurrence of mussel with different effectiveness. The use of some methods is not appropriate due to their impact on other aquatic animals, in other cases they are not suitable from a structural point of view, or their installation is prevented by the specific layout of the building parts of hydro power stations. Also that is why we closely cooperate with experts when fighting the mussel. The Czech native, Renata Claudi, a Canadian expert, was willing to share her knowledge. We are also in contact with the staff from the Faculty of Natural Sciences of Palacky University in Olomouc
It is very important to understand how to combat this animal in an effective way. Sometimes people do more harm than good in their actions that may have a good intention. For example, in the Czech Republic in the 1990s, divers and holidaymakers in particular, deliberately deployed mussels to the lakes in quarries, which were created by flooding pits after mining sand (Naklo pri Olomouci, Chomutov, Tovačov, Otrokovice, water management reservoir Švihov) to “clean“ the muddy water. Although the mussel “did its job” here, but the lakes subsequently got grown with algae and the local ecosystem was completely disrupted. Moreover, during the 1997 floods, the mussel spread to the catchment areas along the whole Morava river.
