An unintended consequence of New York's new clean water is a return of destructive marine borers

"Shipworms" are a menace, devouring the wood in ships and docks. For a while, as the New York Times explains, the pollution in New York harbor actually had some benefit in fighting them:

By the 1960s, the waters had become overrun with raw sewage and oil and chemicals discharged by factories. "Industries were using the harbor as a dumping ground," Mr. Goldstein said. "You wouldn't want to swim or eat the fish, and only the bravest would take out a kayak."

Indeed, there were stories of boats being taken into the polluted harbor just to clean off any marine borers from other waters.

The good news is New York waterways are increasingly clean thanks to laws like the the 1972 Clean Water Act. But the bad news is the clean water has allowed marine borers to flourish:

Marine borers took out a heavily used Brooklyn footbridge over Sheepshead Bay in 2015, requiring the city to close it for several months to repair a hole-ridden foundation. The borers have also weakened timber pilings under the Carroll Street Bridge over the Gowanus Canal in Brooklyn, and under the F.D.R. Drive in Manhattan.

Along the New Jersey waterfront their handiwork led most notably to the partial collapse of a pier at Frank Sinatra Park in Hoboken.

Now the city is spending massive amounts to fight the pests, including $114 million to coat the 11,000 timber pilings under Brooklyn Bridge Park with epoxy.

(Image of Teredo navalis from Popular Science Monthly, September 1878 and Wikipedia.)