Oligotrophic upland lakes

Mountains arise as geological plates clash pushing up the land into dramatic structures, which are then eroded by running water and glaciers. The dramatic structures also persist underwater so lakes are often deep - and cold. The rocks are usually acidic - with granitic or gneiss bedrock.
The cold acidic landscape is typically infertile with any nutrients diluted by this deep lake. Furthermore phosphorus, typically the most limiting nutrient in these ecosystems, may be further inaccessible due to the coprecipitation with aluminum under acidic conditions. They are thus low nutrient, oligotrophic, lakes.
With little decomposing organic material and some stirring by the wind at least the surface layer is oxygen rich. There is little sediment or plankton so the water is crystal clear.
So cold, clear, acidic, nutrient poor, oxygen rich water. With little sediment the shores tend to be stoney. Plants are few, but some specialised flowering plants grow, like the water lobellia in this sheltered bay. The specialised animals typically have low metabolism and grow slowly. The fish are often salmonids, here this years brown trout, who are really titchy, are feeding amongst the rocks.
Filmed Llyn Idwal, in North Wales, which isn't an especially deep lake

[@Likemusicat4]

It would be great to have a summary slide at the end of the video just to re-affirm the key points. Otherwise I love these videos, they feel like I'm on an undergraduate field course again

[@luquest1848]

Stickle Tarn? I once saw "wind rows" on the surface on a blustery spring day