Yachtsmen going out to their boats in Devon’s River Tamar run the risk of rowing through radioactive water following the leak of 61 gallons of toxic coolant from a Royal Navy nuclear submarine.

The coolant was being drained from the nuclear submarine HMS Trafalgar’s reactor into a shore -based effluent tank at Devonport Naval Base when the drain hose burst.

The spillage contained tritium, a substance that can cause burns, cancer and DNA mutations as it breaks down.

It is the worst radioactive leak at a naval base for 23 years. A Royal Navy spokesman said the environmental risk is ‘negligible.’

The submarine is due to be decommissioned next year.