Definition of "weir"

The weir must not represent a physical barrier to fish migration, both locally and throughout the whole river system. If necessary, a fishway is included in the weir.

1997, J. H. L'Abée-Lund, J. E. Brittain, “Weir construction as environmental mitigation in Norwegian hydropower schemes”, in Hydropower '97, pages 51–54

A walkway over the weir is likely to be useful for the removal of floating debris trapped by the weir, or for working staunches and sluices on it as the rate of flow changes.

2010, Sathesh Gopi, Basic Civil Engineering, page 303

The weir catch of mackerel at Monomoy and along Cape Cod has been a failure.

1887, W. A. Wilcox, “58-New England Fisheries in May, 1886”, in Bulletin of the United States Fish Commission, volume VI, published 1886, page 191

For a spell we done pretty well. Then there came a reg'lar terror of a sou'wester same as you don't get one summer in a thousand, and blowed the shanty flat and ripped about half of the weir poles out of the sand.

1913, Joseph C. Lincoln, chapter 1, in Mr. Pratt's Patients