Mike Dilger's Wildlife Watching

In his series of great places to watch wildlife in the UK, the star of BBC One’s The One Show this month advocates spending time around the peaceful bodies of fresh water dotted across the country.

Mike Dilger

We call them lakes in England, lochs in Scotland, llyns in Wales and loughs in Ireland, but a feature all these waterbodies share is their natural origin. This puts clear water, as it were, between them and those waterbodies with decidedly anthropogenic beginnings, such as reservoirs. But when does a lake, llyn, loch or lough become a pond, and vice versa?

Well, according to limnologists, who study freshwater habitats for a living, the strict definition should not be based on the size of the waterbody, but on its depth. Ponds, for example, are shallow enough to allow rooted plants to conceivably grow right across their surface. This ‘photic zone’ is where the sun’s rays are able to penetrate right to the bottom. By contrast, their deeper cousins will also incorporate an ‘aphotic zone’, which extends downwards sufficiently far to prevent sunlight reaching the bed.

Lakes, lochs and so on additionally tend to have distinct layers of warmer and colder water, particularly in the summer months, while pond temperatures tend to be more consistent throughout. Finally, if the water body is only ever capable of producing small wavelets, on even the windiest day, then it should definitively be placed into the ‘pond’ category.