English: Water End Swallow Holes: Sinkhole basin Please see 990507. This is the sinkhole basin where surface water accumulates to form a lake during times of flood. As the flood recedes the floodwater gradually drains back into the natural sinks. This is also effectively the source of the River Colne which eventually flows into the River Thames here 95711 and here 480636. Someone has considered it to be a good idea to throw an old chair and a large broken plastic container into the middle of the basin.