Lake Whakamaru runs east-west and lies downstream of Lake Atiamuri. It is part of the Waikato River system.
It was formed in 1956 when it was dammed for hydro-electricity generation. It is probably the shallowest of all the hydro-electric lakes on the Waikato River system and so warms up during the summer.
The South Waikato District Council maintains the Whakamaru Reserve at the southern end of the lake; this is a popular freedom camping spot during summer. There is excellent access to the river for fishing and recreation along the northern bank as State Highway 30 follows the lake for almost its entire length.
The road crosses over the dam itself and the small side road provides access to a reasonable section of the southern bank. There are a number of good boat ramps on the lake. The popular Waikato River Trails runs through this reserve to the north west and south east.