From the Commonwealth of Massachusetts Division of Fisheries and Wildlife...

Big Alum Lake
Located in Sturbridge, this lake averages 23 feet in depth with a maximum of 45 feet.  Transparency is high at 17 feet.  The pH is on the acidic side at 6.4.  Aquatic macrophytes present include pondweed, yellow water lily and muskgrass.

Fish Populations - Big Alum was sampled to assess the fish population.  Eight species were found, including rainbow trout stocked in the spring.  Gamefish collected, besides the trout, included smallmouth bass and chain pickerel.  Panfish present included bluegills, pumpkinseeds, redbreasted sunfish, yellow perch and brown bullheads.

Fishing - Big Alum is stocked each spring with rainbow trout and brown trout.  This attractive lake draws a considerable number of anglers interested in catching trout from mid-April through early June. Spring smallmouth bass fishing should be good, as this lake presently supports a healthy population.

Trout do hold over through the summer and are caught in the fall and winter.  Both rainbows and browns can be taken. For those interested in ice fishing, Big Alum also contains impressive size chain pickerel. Jigging for yellow perch should also be productive.