Many people have heard of "school catchment areas" meaning the areas of towns and villages from which schools recruit their pupils.
'Catchment' means a similar thing when referring to ecology and geography. In this context, a catchment is the area of land, including the hills and mountains, woodlands, and buildings which water drains from, before flowing into the streams, rivers, lakes and tarns.
For example the Windermere Catchment includes rivers such as the Rothay, Brathay and Troutbeck, as well as tarns and lakes including Grasmere, Rydal Water, Esthwaite and Elterwater.
The map below shows the catchment area in a lighter white and grey: