Brook trout
Naturally, multiple fish species inhabit the river. Brook trout, chain pickerel, and largemouth bass are common. The Massachusetts Division of Fisheries and Wildlife stocks brook trout in the Assabet's tributaries, including the above-mentioned Elizabeth Brook, though there are existing natural populations. Chain pickerel live in weedy areas along the Assabet. Largemouth bass thrive in the Assabet Reservoir and in the calm waters before Hudson. Other native fish one may encounter on the Assabet include American eel, black crappie, brown bullhead, golden shiner, northern pike, pumpkinseed, white sucker, white perch, yellow perch, and a few other small species.