Algal Bloom Health Warning Issued for Pegasus Lake

Published: 07-Jan-2020

Lake Pegasus is now off-limits for swimming, after the Canterbury District Health Board today issued a public health warning following the discovery of potentially toxic blue-green algae (planktonic cyanobacteria) in the water.

Warning signs have been put in place around the lake notifying passers-by of the health danger posed by the water.

While the lake has been impacted on by algal bloom in the past, it had enjoyed a clean bill of health this summer, up until today’s warning notice.

The algae look like dark brown to black mats and can produce toxins harmful to people and animals.

Environment Canterbury are responsible for testing river water quality. They conduct weekly testing of the most popular swimming spots over summer and you can view the results and find out if it’s safe to swim here (

Lake Pegasus is being monitoring on a weekly basis and the public will be advised of any changes in water quality.

Facts about cyanobacteria:

  • The algae occur naturally but can increase rapidly during warmer months.
  • If the water is cloudy, discoloured, or has small globules suspended in it, avoid all contact.
  • Not all cyanobacterial blooms are visible to the naked eye and toxins can persist after the blooms disappear.
  • Cyanobacterial concentrations can change quickly with changing environmental conditions (e.g. wind). If a health warning is in place avoid contact with the water

Learn more:

Toxic Algae Information Brochure

Toxic Algae FAQs

Name: Community and Public Health

Phone: (03) 364 1777