in the kiel canal, the gobies have eliminatad practically every other fish that breeds there but the nest-protecting zander(walleye) that feeds on them. There is no other fish but goby, zander, trout and eel which breed elsewhere. Not cool.
Same goes for the country´s biggest river, the rhine. With practically every river system connected by canals and ship traffic, its just a matter of time before they spread the continent.