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Some notes on lake data definitions

Size and altitude

All measurements for the size of the lake (perimeter, surface area, maximum fetch and Shoreline Development Index), as well as the altitude, relate to normal water conditions. Some lakes will be considerably smaller in times of drought, and may even be close to non-existent. Equally, at times of increased rainfall floodwater may extend the surface area and perimeter of some lakes significantly.

Location data

Except where otherwise stated, all location data (latitude, longitude, OS grid reference and local authority/region information) relates to the centre of the lake. Some larger lakes may be bordered by more than one county or local authority, but only the one which is nominally responsible for the centre of the lake is shown.

Maximum Fetch

The maximum fetch of a lake is the longest uninterrupted distance over water in a straight line.

The lake with the longest fetch is not necessarily the largest lake in terms of either area or perimeter, as the shape of the lake makes a difference. But, on the whole, larger lakes have larger maximum fetches.

Shoreline Development Index

The Shoreline Development Index is the ratio of the length of the perimeter to the circumference of a circle with the same area as the lake. The more irreglarly shaped the lake, the higher the Shoreline Development Index will be. A perfectly circular lake will have a Shoreline Development Index of precisely 1.

For comparison, the lake in this database with the lowest Shoreline Development Index (and hence that most closely approximates a circle) is Dubh Loch in Tayside, while the most irregular lake is Loch Scadabhagh on the island of North Uist in the Outer Hebrides.