Kerry County Council says there has been a reduction in the amount of algal scum in Lough Leane.
Algal scum, which is particularly harmful to dogs, was found along the shoreline of the lake near Muckross Abbey last month.
Tests conducted in recent weeks show the presence of algal scum has diminished, while a test carried out last week found no traces among the samples taken.
Kerry County Council says tests will continue to be carried out, both along the shoreline and on the lake, until the end of September.
Warning signs advising walkers and bathers of the potential for algae during the summer months remain in place along the shoreline.