The character of these rivers is mainly determined by climate and topography. Scotland's high rainfall, low evaporation and lack of extreme temperatures create rivers with a large flow relative to the size of the catchment, a dense network of rivers and burns, and moderate water temperature fluctuations. Scotland's largely mountainous topography results in energetic, steeply flowing, rivers with beds of coarse material - gravels and boulders (e.g. the River Dee in the Eastern Cairngorms). Scotland also has slower flowing, more silty, river stretches in the lowlands (e.g. the lower River Endrick), but these are not typical of the majority of rivers in Scotland. As a general rule, the main east/west watershed is close to the west coast. Hence most of the rivers flowing to the west are short and have steep gradients compared to the longer, more gently graded east flowing rivers.
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Lochs and Lochans. Because standing waters are characterised by a lack of water flow, conditions in them are normally much more homogeneous than in running waters. They may reach great depths, but most have simple, often broad, basins. Whilst erosion does occur in standing waters, it is only severe on exposed shores and eroded materials usually remain within the same basin. In addition, materials from inflowing streams are constantly being deposited, tending to fill in the basin and eventually obliterate it completely.
Standing waters are classified as shown in Box 4.2. The great majority of Scotland's lochs are oligotrophic; a typical example is the deep, clear Loch Morar. Eutrophic lochs are relatively uncommon in Scotland and occur mainly in the Lowlands. They are naturally rich in nutrients, which can lead to them having lush shore vegetation and blooms of algae which can use up most of the available oxygen in the summer months and hence affect fish and other aquatic life. Mesotrophic lochs contain enough nutrients to support rich and diverse plant growth while usually remaining clear; they are not dominated by algae.
