HIDDEN pollution in streams, ponds and rivers is being revealed by have-a-go heroes.

Dangerous nitrates and phosphates in freshwater across Oxfordshire are being uncovered each year by volunteers in the Thames WaterBlitz.

Now organisers have called on nature lovers to dive into the next citizen science survey on Tuesday, May 2.

Project co-ordinator Luis Velasquez, of Oxford's Earthwatch Institute, said: "The past three events have been hugely successful thanks to efforts of local school groups and general public who carried out simple tests of water around their home or office, but we need more help.

"Each WaterBlitz provides information from areas that would otherwise not be monitored and shows seasonal impacts of climate and land use change are important."

Anyone in Oxfordshire can order a free water testing kit online.

The actual process of taking a sample takes seconds, and data from any pond, river or stream in the county can be invaluable.

Since it launched in autumn 2015, Thames Waterblitz volunteers have collected a total of 1,208 samples and last year more than 200 people in Oxfordshire helped out.

The results have revealed nitrates and phosphates into the county's biggest rivers including the Thames, the Ock, the Glyme and the Evenlode.

These chemicals, which get into the river system from fertilisers on farmers' fields, act as super fuel for algae, essentially pond weed, in the water, which causes algae to explode in what is known as an algal bloom.

This mega-algae leaches all the oxygen from the water, suffocating other plants, fish and insects there and downstream.

Higher levels of nitrates can also be harmful to humans (the World Health Organisation guide limit is 50mg of NO3 per litres), and water companies have to ensure water is safe to drink.

By identifying areas where nutrient discharges are more likely, Mr Velasquez said the WaterBlitz was helping regulatory bodies like the Environment Agency, research institutes and river trusts to improve waterways and reduce the risk of harmful pollution.

The Thames WaterBlitz is part of Earthwatch's FreshWater Watch project, a global study of the health of freshwater ecosystems.

Mr Velasquez said: "It is a novel and groundbreaking project.

"Through the participation of hundreds of volunteers in Oxfordshire and the rest of the Thames river basin, nutrient pollution hotspots (nitrate and phosphate) and clean water sites have been identified.

"These results are helping Oxford communities and national stakeholders to better understand the freshwater environment around us."

Find out how to join in this year's blitz online at wildoxfordshire.org.uk/waterblitz or call Wild Oxfordshire head office on 01865 407034.