Health warnings are in place for six lakes near Hamilton due to an increase in cyanobacteria levels brought on by recent warm weather.
The lakes - Whangape, Waikere, Kainui, Hakanoa, Waahi and Ngaroto - are shallow and have a history of algal blooms in summer.
The Medical Officer of Health, Dr Dell Hood, says contact with the lake water can result in rashes, skin and eye irritation, allergy symptoms and stomach upsets.
No swimming in Lake Tutira
The Hawke's Bay District Health Board is warning visitors to the region not to swim in Lake Tutira, north of Napier.
A week ago on Saturday the board's public health unit issued a warning after water monitoring showed the presence of a cyanobacteria algal bloom.
Health Protection Officer Joanne Lynch says the past week's hot weather means the bloom is still present.
She says there are signs around Lake Tutira warning people against swimming or canoeing.
Water samples from the lake will be tested again early next week.