A group of 60 researchers, managers of the public administration and students will meet on Thursday and Friday September 28 and 29 at the University of Navarra to discuss the ecological quality of water in rivers, lakes and reservoirs.

Also, in the meeting there will be different talks about the threats that inland waters are currently suffering, such as the growing presence of invasive species that endanger local species. According to the organizer of meeting, the professor of department of Environmental Biology and expert in freshwater species Rafael Miranda, "this problem is of such magnitude that invasive species currently outnumber native species in rivers, lakes and marshes of the Ebro axis".

Among them, the most abundant and dangerous are the blackbass (or American perch), the pike and the catfish, all of them exotic predatory and aggressive species "which are also being continuously introduced into our lakes and rivers. Without going any further, after the recent cleaning of the lakes of Mendillorri and Sarriguren we can already observe specimens introduced again in these ecosystems. And they are certainly not species that are relegated to city lakes, but are also being introduced into rivers, such as the Arga, with the idea of using them later for recreational fishing", warns the expert.

But when is a species considered invasive?

Another example of an introduced species that has become dominant in the new habitat it occupies is the bleak. "This Central European fish was introduced as live bait, it is believed, in a small river in the Catalan Pyrenees. This happened in 1992, and 25 years later this species is the most abundant in the Ebro basin," warns Professor Miranda. Something similar happened with the catfish -an aggressive predatory fish that can measure up to one and a half meters and weigh up to 90 kilos-. "A few years ago they were looking for locations to record the largest specimens of catfish in the world and they recorded them in Mequinenza (Zaragoza) where they located a specimen that exceeded two and a half meters and weighed 100 kilos".

"One of the issues that underlies when we deal with invasive species, and which we will also address in this congress, is when we call an animal exotic and when we consider it native." For example, he says, today we know that all of the earthworm species living in North America are actually European and were brought over by early settlers. "Another example might be the turtle dove, which as its name suggests is native to Turkey. Through a semi-natural phenomenon this bird has colonized the whole of Europe in the last century. Would it make sense to exterminate it today?", asks the organizer of meeting, professor at the University of Navarra Rafael Miranda.

• conference on Ecological Quality and Conservation Status of Inland Waters