The lake at Pugneys Country Park has reopened this week, more than a month after its sudden closure.
The lake was closed on Tuesday, August 6, after high levels of the dangerous blue green algae were detected in the water.
Green algae can cause rashes and irritation in humans, and can be toxic if ingested by animals, even in small quantities.
Visitors to the park were asked to avoid the lake - and keep their dogs from swimming in it - while the algae cleared.
A popular tourist spot, the park attracts thousands of visitors each year. Water sports and other activities are often held in the park.
The lake reopened on Wednesday, September 11.