Cooling lake changing colour

As the days get shorter and rainier, Virginia Lake will slowly return to normal.

The lake, which turned a soupy green colour over summer due to algal bloom, is being regularly tested by the Whanganui District Council.

"The council samples and analyses Rotokawau Virginia Lake weekly to check the algae cell densities," senior wastewater engineer Arno Benadie said.

"The lake reached its peak algae bloom at the end of February 2016 and the cell densities have been declining steadily since then."

The algae appeared because conditions were ideal for them to grow, but as the temperature lowers they will begin to disappear.

"The algae blooms are dependent on the water temperature in the lake and the available sunlight, so it will depend on the weather and the amount of sunlight hours as summer comes to an end, as to how quickly the bloom declines.

"The more it rains, the quicker the water in the lake will cool down."