Lake Rotoiti, Tasman

Infobox lake
lake_name = Lake Rotoiti
image_lake = Lake Rotoiti and St Arnaud in 1969.jpg
caption_lake = Lake Rotoiti and the St Arnaud Ranges in 1969
image_bathymetry =
caption_bathymetry =
location = Nelson Lakes National Park, Tasman Region, South Island
coords =
type =
inflow = Travers River
outflow = Buller River
catchment =
basin_countries = New Zealand
length =
width =
area =
depth =
max-depth = 82 m
volume =
residence_time =
shore =
elevation =
islands =
cities = Saint Arnaud

Lake Rotoiti is a substantial mountain lake within the borders of the Nelson Lakes National Park. It is fed by the Travers River. The greatest depth is 82 metres and it is surrounded by beech forest. Saint Arnaud is a small community at the northern end of the lake. The water from the lake flows into the Buller River.

Tramping tracks circle the lake, including the Lakehead track on the east side and the Lakeside track on the west side of the lake. There is also a water taxi service that travels the length of the lake to ferry trampers to and from the Coldwater and Lakehead huts at the head of the lake. The lake is also a popular place for waterskiing and is adjacent to Mt Robert, which hosted a small club-owned skifield, until it was removed by DOC in 2005.

The lake has introduced trout which attract recreational fishermen.