fossé à poissons

CONT: By placing the hatchery tanks in a pond near the river, the [angler association] designers ... created a moat to protect their [fish] stock. In order to assail the fish tanks, a would-be thief must cross 10 feet of moat, which stays at a cool 12-13 [degrees Celsius] even in the hottest part of the summer at a depth of three feet.