From the Wikipedia page:
"The Polish government said that the perpetrators would be severely punished, however also blamed uninvolved opposition politicians Donald Tusk, Rafał Trzaskowski and compared the situation to other previous unrelated events in Warsaw and Gdańsk, where the opposition Civic Platform hold power. Grzegorz Witkowski, a government minister, as well as repeating the unfounded government claims, also blamed ecologists and stated that the river is safe to enter."
Grzegorz Witkowski is trying to bring back a pre-Gorbachev style of Communist communication. "The problem isn't that the river was poisoned, the problem is that ecologists have told people the river is poisoned."