southdown ponds

Visitors to Harpenden Common may have noticed a biofilm and algal blooms on the surface of the Southdown Ponds recently which looks “oily” alongside clumps of green algae. This is something that is more noticeable during periods of low rainfall and high temperatures.

Biofilm is a natural occurrence caused by bacteria feeding on decaying organic matter such as leaves, algae and animal waste. During periods of low rainfall and hot weather the rate of decomposition of organic matter is much faster which creates conditions conducive to microbial blooms.

The Southdown Ponds were created as attenuation ponds, specifically designed to control stormwater flow from the High Street and local houses, and settle out the pollutants within. As a result, these ponds are of a lower water quality than other natural ponds. In 2007 an oil interceptor was installed to help with this process and improve the quality of the ponds themselves.

Our Green Spaces team carefully manage the many ponds and waterways across Harpenden. We also contract external specialists to test the water quality to ensure that it is within the required levels. The Southdown Ponds were tested earlier this month and we were advised that no action was required. If you would like to read more about Harpenden’s green spaces and our management plans, please visit: www.harpenden.gov.uk/green-spaces