The other day, Adam Castiglioni spotted a lot of dead fish floating in the Charles at the Museum of Science and wondered what's up with that.
Fish kills are a natural and regular occurrence but you can report one to @MAEnviroPolice so that it can be checked on.
Most likely, it's the start of the annual pogie migration out to sea and the annual pogie die-off, often caused by reduced oxygen levels in the river caused, in part, by the sort of high temperatures we've been having of late (and algae blooms).
Charles River pogies - also known as menhaden - breed further upstream, then swim (or try to swim) back out into the ocean.
Overfishing had depleted pogie stocks in Massachusetts waters; then the state banned pogie fishing and their numbers rebounded.