A week ago, there was one koi swimming around at the north end of Jamaica Pond. Today there were at least five, and maybe six - two orange ones, a mostly white one and one or two sort of mud-colored ones.
They're cool to look at, but the problem is that, left unchecked, they can quickly out-compete the species that the state releases into the pond each year, causing problems not just for the fish but for the birds - and even turtles that eat fish.
Also, they eat the plants that help filter the water. Oh, and they can live for up to 50 years.
As the New York Times reported about carp infestations in the Midwest:
Where they invaded, lakes turned brown and muddy. Plants and ducks disappeared. They displaced other fishes and dominated. ...
When they forage for bugs and seeds on lake bottoms, they stir up sediment, uproot plants, change water chemistry, promote algal blooms and leave little food for waterfowl.