The lake is located in Hofshreppur in Skagafjörður. Its original elevation
above sea level was 97 meters, but after the construction of a hydropower
plant the water level rose significantly. The lake now covers an area of
approximately 3.9 km², with a maximum depth of about 23 meters.
Several rivers and streams flow into the lake, including Tunguá, Fljótaá,
Húnstaðaá, Húnstaðalækur, Stórilækur, and others. The outflow runs northward
through the Fljótaá river. A dam built below the lake as part of the power
station has caused substantial changes to both the size of the lake and
its surrounding environment.
Stífluvatn is known for its abundant and high-quality fish stocks. The lake
contains only Arctic char, a self-sustaining local population. The fish can
grow quite large, sometimes reaching up to six pounds. The stock is
considered to be in fairly good balance, although it is often suggested
that fishing pressure could be increased.
During summer, the area around Stífluvatn is exceptionally beautiful, with
few places comparable to its scenery. The lush vegetation, shaped by the
short but intense northern summer, and the midnight sun near the horizon
create a striking atmosphere. It is often said that people reflect the
environment in which they are raised.