Cornwall's largest natural freshwater lake is being surveyed by divers for the first time. Scientists have previously only studied Loe Pool in Helston by boat.
They hope a dive study of plant life will help them find out more about the ecology of the site. It's part of a four year research project funded by Natural England.
Loe Pool has suffered from algal blooms for around 40 years, caused by run off from the valley above. The National Trust, which manages the site, says improvements to the local sewage treatment works has helped improve water quality which means divers should have better visibility under the water.
Local folklore suggests the pool may have been where Sir Bedivere, a Knight of the Round Table, cast King Arthur's Sword Excalibur into the lake.