There’s nothing so satisfying as splashing in a river, but have you ever taken a closer look to see what lives there? Although in Cambridgeshire there is a good chance you’ll find otter, water vole, kingfisher and fish such as bullhead and minnows even in a small stream, today we were looking for invertebrates. Because they vary in their habitat and water quality needs, invertebrates can tell you a lot about how healthy your river is.

Sometimes the smallest creatures can be the most fascinating. We watched flatworms, with their almost cat-like heads, glide over the bottom of our tray – these amazing creatures can regrow lost body parts, including their heads. We tried to count the miniscule eyes of tiny leeches, to see which family they belonged to, while they looped and wriggled and refused to stay still. We identified families of caddis larvae by the shapes of their cases and of the creatures venturing their heads outside, and marvelled at the variety of materials and designs. And we tried to catch the speedy mayfly larvae and the graceful (but also speedy) lamprey amocytes.

Freshwater invertebrates can be easily identified as broad groups with a simple guide (e.g. the FSC Freshwater Name Trail), but getting to family or species level can be more involved and tricky.... Or you can just watch them and enjoy. It's a great way to get a glimpse into a hidden underwater world. You might need a magnifying glass, but prepared to be amazed!