The weir for the purpose of navigation need not be in any way different from the milhweir, otherwise than that, instead of an intake sluice, there must be a lock (q.v.) with upper and lower gates, and a chamber between them as long and as wide as the largest vessels navigating the river. Fishing-weirs are generally provided with a sort of cage, called in Scotland a cruive, a word which has been made English by having been used in English fishing acts. The cruive consists of a chamber generally about 4 or 5 ft. in width, and as much or a little more in length, having at the upper end a portcullis grating, called the heck, with the bars vertical and 3 in. apart, so as to let small fish get through, and at the lower end two folding horizontally sparred doors called the inscales, pointing upward, but set so as to leave a small opening between the points, through which the ascending salmon enter. Partly from the inward pointing of the inscales, and partly from the instinct of the fish to ascend the river, they seldom get out again, and are easily caught. Frequently, weirs serve the purpose both of mill-dams and of fishing weirs. ' Jw A weir sometimes made use of for catching salmon and other fish in tidal rivers, con sists of a sort of horse-shoe shaped structure of loose stone-work, through which the water can percolate freely, with its heel or open end pointing up-stream. The fish ascend the river with the flood-tide, and falling back with the ebb, part get embayed within the walls at low water, and are either left dry, or are shut in so as to be easily caught.
Weirs, either of stone or of wicker work, are also sometimes made use of as an acces sory to what in English fishing-rivers are called putts and putchers, being a sort of combination of wooden gratings acting something like those of the cruive and net-work; and in many cases, weirs, either natural, as formed by rocks or islands, or strictly arti ficial, are used for catching fish by means of an attached poke-net extended by the cur rent.
By the English common law, no fishing mill-dam or fishing weir is legal except it be ancient, and even an ancient fishing-weir must have a free gap, and every fishing mill dam must have a proper fish-pass.
The following are provisions as to weirs in the English salmon fishery act, 1861: For the purpose of clearly indicating the rights of mill-owners, etc., in the first place, the expression " dam" is defined to mean all weirs and other fixed obstructions used for damming up water; " fishing-weir," dam used for the exclusive purpose of facilitating the catching of fish; and " fishing mill-dam," a dam used partly for facilitating the catch ing of fish, and partly for supplying water for milling, etc. (24 and 25 Viet. c. 109, a. 4).
The following regulations are to be observed with respect to dams: No darn, except such weirs and fishing mill-clams as were lawfully in use on Aug. 6, 1861, by
grant, charter, or immemorial usage, must be used for facilitating the catching of salmon. Any proprietor of a fishery, with the consent of the home office, may attach to every dam which existed on Aug. 6, 1861, such a fish-pass as the home office may approve, so that no injury be done to the milling power, or to the supply of water to or of any navi gable river, canal, or other inland navigation. Every person who, in waters where salmon are found, constructs a new dam, or raises or alters, so as to create increased obstruction to fish, a dam already constructed, must attach and maintain in an efficient state such a fish-pass as may be determined by the home office. By the Tweed act, mill dams, weirs, caulds, and other permanent obstructions are to be so constructed as to permit the free run of salmon in the ordinary state of the river. In Ireland, as in England, weirs are legal, if they can be traced back to statute 25 Edward III. Special fishery commissioners have power to inquire into legality of all fishing weirs, and every fishing weir must have a free gap.
By the old Scotch law, a provision as to mill-dams is given in the act 1696, as fol lows: " In respect that the salmon-fishing within the kingdom is much prejudiced by the height of mill-dams that are carried through the rivers where salmon are taken, his majesty, with consent of the estates of parliament, orders a constant slope in the mid• stream of each mill-dam dyke; and if the dyke be settled in several grains of the river, that there be a slope in each grain (except in such rivers where ernives are settled), and that the said slope he as as conveniently can be allowed, providing always the said slope prejudge not the going of tire mills situate upon any such rivers.' Cruives arc by various old acts declared to be illegal in tidal waters, except the eruives and yairs of the Solway, which is exempted as being a border river.
By the Scotch fishery act of 1862, the commissioners arc empowered "to make gen eral regulations with respect to the construction and alterations of mill-dams, or or wafer-wheels, so as to allow a reasonable means for the passage of salmon ;" and they made a by-law, which has been sanctioned by the home secretary; providing that every dain should have a salmon pass or ladder, and also making provision for Leeks at the intakes and lower ends of the;gill-lades, and immediately above the wheels, and regula tions whereby the water, when not used for the mills, should be sent down the natural channel of the river. The commissioners are also required to make, and have made, general regulations as to the construction and use of cruives, which implies their legality, but only where there is a prescriptive right.