Weir :  (noun)
1: a low dam built across a stream to raise its level or divert its flow
2: a fence or wattle built across a stream to catch or retain fish

aboideau, air lock, arch dam, avenue, backstop, bamboo curtain, bank, bar, barrage, barrier, bear-trap dam, beaver dam, blowhole, boom, breakwater, breastwork, brick wall, buffer, bulkhead, bulwark, channel, chute, cofferdam, dam, debouch, defense, dike, ditch, dock gate, door, earthwork, egress, embankment, emunctory, escape, estuary, exhaust, exit, fence, flood-hatch, floodgate, flume, gate, gravity dam, groin, head gate, hydraulic-fill dam, iron curtain, jam, jetty, leaping weir, levee, lock, lock gate, logjam, loophole, milldam, moat, mole, mound, opening, out, outcome, outfall, outgate, outgo, outlet, parapet, penstock, pore, port, portcullis, rampart, roadblock, rock-fill dam, sally port, seawall, shutter dam, sluice, sluice gate, spiracle, spout, stone wall, tap, tide gate, vent, ventage, venthole, vomitory, wall, water gate, way out, wicket dam, work,