Signs are up at one of Whanganui's safest and most gentle swim spots - Lake Wiritoa - warning people not to touch or drink the water.
They follow signs put up at Dudding Lake in recent weeks, and permanent health warning signs put up at three coastal streams north of Whanganui - the Mōwhānau, the Kai Iwi and the Ototoka.
The two lakes and the streams have been popular spots for swimming - especially for children, who are more at-risk from poor water quality.
Read more: Algae levels push Dudding Lake close to 'flipping' - council told
Health-risk signs are now up at Lake Wiritoa because the level of blue-green algae has climbed to twice the maximum level recommended for swimming.