The Charles River supports a diverse community of fish, including over 25 species of resident freshwater fish and a host of anadromous species. Anadromous fish are born in freshwater, spend most of their lives in the ocean and return to freshwater to reproduce. They depend on the river for spawning habitats during their dramatic spring runs.
Collectively known as river herring, alewife and blueback herring are two of the most well-known anadromous fish in the Charles.
In fact, the Charles River supports one of the largest blueback herring runs in the Commonwealth. River herring can typically be observed spawning in the river from mid-May to mid-June. Rainbow smelt, however, are the first to arrive each spring, when spawning begins in mid-March below the Watertown Dam. American shad and white perch also use the river for spawning habitat, whereas striped bass enter the Charles to feed.
Unlike anadromous species, catadromous fish are born in the ocean and travel to freshwater habitats to feed and mature. The American eel is a prime example of this, and each spring tiny juveniles or “glass eels” can be found moving up the Charles.