When sodium cyanide leaked into a Walsall canal this month, leading to major incident being declared and miles of the waterway closed off, the Canal & River Trust was working in uncharted territory.

The charity is used to fighting pollution in the waterways that crisscross the country, but this type of chemical – and the extreme risk to public health that came with it – was not something it had tackled before.

“I’ve never known an incident like this in 20 years of pollution incidents on the canals,” said Karen Jackson, a contamination officer. “It’s not like when we’re dealing with oil or farm pollutions, where we know exactly what we need to do. With this, it’s unprecedented. We’re looking at lots of options but the fear is they may not be fully effective, and some are incredibly expensive.”