[2] Mashapaug Lake is natural in origin, but the construction of two dams has raised its water level.

Water flows over the Bigelow Brook dam at the southern end of Mashapaug Lake at all times of the year.

[2] The majority of Mashapaug Lake's bottom consists of gravel and sand, with some scattered boulders, trees, and stumps.

In the deep, flat areas of the lake's bottom, fine sand, silt, and organic muck can be found.

Visitors can access the Mashapaug Lake through Bigelow Hollow State Park at its southern end.

Some plants that can be found in the shallows are yellow pond-lily (Nuphar variegata), pickerel weed (Pontederia cordata), and pondweeds (Potamogeton spp.).