River Yealm

Yealm is a river in the Dartmoor moors in Devon in south-west England. It rises 1,411 feet above sea level on the Stall Moor mires of south Dartmoor and makes a 12 mile journey to the sea, passing through Cornwood, Lee Mill and Yealmpton, before reaching the estuary mouth just below Newton Ferrers and Noss Mayo.

This short river once supported relatively large stocks of salmon, sea trout and brown trout but their populations have dwindled since the 1940s.

The Yealm estuary has a large oyster bed. The fertility of estuaries relates to the fact that when different water masses meet there is usually a bloom of the phytoplankton, which can double its numbers/mass every 24 hours, but nude microscopic algae multiply so quickly they can consume all the available plant nutrients until one nutrient is absent and they return to dormancy. But when two bodies of water meet, as they do in estuaries, it is unlikely that the same nutrient is missing in both. Here, the River Yealm and its estuary are well-matched, so the fresh and sea waters mix in approximately ideal proportions while there is always a reservoir of blooming mixed water that is not washed out to sea at low Spring tides. Some other South Devon estuaries do not share this feature: some, like Salcombe, receive too little fresh-water while some, like the Dart receive too much, at least for ideal shellfish production.

Cockles and wild oysters can be found on the shore at low tide in the right season.