Namsvatnet is a substantial body of water by any measure: roughly 39 square kilometres of surface, seventeen kilometres long and about four across, 455 metres up, 84 metres deep at its deepest and averaging 28. Its catchment covers some 700 square kilometres. Since 1959 it has also been a reservoir, holding 458 million cubic metres of usable storage, and a tunnel now carries part of its water south toward the Vektaren reservoir instead of letting it run its old course. The river Namsen used to be the lake's primary outlet, and the Namsen still begins here — but a river whose headwater is a regulated reservoir is a river on someone else's schedule. Fourteen metres of vertical drawdown leaves a visible mark: a bathtub ring of bare, scoured shoreline that widens through the winter and drowns again in spring.

The water arrives from the northeast, out of Børgefjell National Park. Three main streams feed the lake: Storelva, draining the lake Jengelvatnet; Virmaelva; and Orelva, coming down from Ovrejaevrie. Børgefjell itself was protected in 1963 and now covers about 1,447 square kilometres of Trøndelag and Nordland along the Swedish border — a park deliberately left almost untouched, with very few marked trails and almost no visitor facilities, where a walker can go days without seeing another person. It is best known as a stronghold of the Arctic fox, though wolverines are the more numerous large carnivore, and golden eagles and rough-legged buzzards work the open ground. All of it is grazed by domesticated reindeer, as it has been for centuries.

Three fish species share the lake: Arctic char, trout, and the small silver cyprinid Norwegians call ørekyt — the European minnow. The char is the one the district is named for, since the municipality of Røyrvik takes its name from an old farm whose name means, plainly, char inlet, and it is the species best suited to cold, deep, nutrient-poor northern water. The minnow is the complicated one. It is native to parts of Norway, including some watercourses in the old Nord-Trøndelag county, but across the twentieth century anglers using it as live bait carried it into every county in the country. It now sits in the very high risk category of Norway's alien species list, because in lean water it outcompetes trout fry along the shoreline. Anglers keep coming regardless, and tourism has become one of the steadier economic activities on a lake whose other industry is measured in megawatt-hours.

There is no road along the length of Namsvatnet. From Namsvassgrenda at the southern end, a boat service runs about nine kilometres up the lake to the northern shore, and that crossing is the practical gateway to Børgefjell for anyone not prepared to walk in from a great distance. It also delivers people to Kristi krybbe, which is privately owned and used during the summer months — a mountain chapel on the edge of one of the emptiest landscapes in Europe. The combination is very Norwegian: an industrial reservoir, a wilderness park with no infrastructure, a fifty-seat chapel under a turf roof, and a small boat that connects all three. In Southern Sami the lake is Nååmesjenjaevrie — the name the country wore before the reservoir arrived.