The lake is small and littered with hostile creatures. On the west bank there is a Department of Water building guarded by some mirelurks. Inside there is a terminal which indicates that the lake is highly irradiated and has been so since before the Great War. The northeast edge of the lake has a small boat ramp and a couple of picnic tables, where a fishing tournament ad can be found. To the north is a bridge, where random encounters may occur. A pair of streams feed into the east side of the lake and host many bloodleaf plants. One of the streams leads to a nest of mirelurk eggs inside the sewage pipe underneath the truck with the partially overturned boat. To the east is radio tower 3SM-U81 which can be accessed by following the road, patrolled heavily by mirelurks. The lake also has a sort of billabong off to the east side. At the center of the lake, there are numerous barrels of radioactive waste. Along the perimeter are several boats and ski-doos, indicating that the water level in the lake was higher in the past. The lake also hides several containers below the surface.
- The water is highly irradiated, as noted in a nearby terminal, due to excessive dumping. With that said, since the "Aquaboy" perk only negates the small dosage of rads from the water itself and not any other sort of contaminants, it will only slightly lessen the high amount of Rads, which increase towards the center, peaking near 120 Rads on Survival difficulty.
- The lake is mentioned regarding the rise of the radiation and toxicity of a fish sample by over 15 times from the previous year, in the Nahant Oceanological Society terminal entries. Well over safe levels for swimming according to the report being returned to the colleague requesting the testing of the Lake Quannapowitt fish.
Lake Quannapowitt only appears in Fallout 4.
- Lake Quannapowitt terminal entries: "Repeated water quality assessment per department request. Contaminant levels have continued to increase. Recommended closing the lake, beginning formal inquiry, canceling the mayor's fishing tournament."
- Nahant Oceanological Society terminal entries: "This is very strange. One of my colleagues sent us a sample from Lake Quannapowitt asking for independent verification to compare against his findings. The radiation and toxicity levels are 15 times higher than the sample we had from last year, and well over safe levels for people to be swimming. I've sent our report back to him to confirm his findings."