Riparian (Lat. ripa, the bank of a river), in law, a term relating to the rights and privileges of persons who own lands lying upon or bounded by streams or rivers. At the common law all bays and arms of the sea, and all rivers wherein the tide ebbed and flowed, were considered navigable, or public highways; and all rivers, irrespective of size, where the tide did not ebb and flow, were unnavigable. The owner of land lying upon an unnavigable stream (in the common law sense) owns the bed of such stream to its centre, or thread; and the grant of a piece of land bounded by a river will carry the exclusive right and title of the grantee to the middle of the river, unless the grant certainly expresses the intention of the grantor to convey only to the bank or margin. If a person owns the land lying on both sides of the river, he also owns the whole river as far as his land extends along it; and the owner in fee of land lying under an unnavigable river, whether he owns the whole bed or only to the centre on one side, may sell and convey such land separate from the upland to which it is attached.

Where a river is actually navigable for boats and rafts, the public have an easement in the water for this purpose, and are entitled to a right of passage up and down, which the riparian proprietors cannot interfere with or prevent; and all obstructions or impediments to the free use of the river in this manner are public nuisances, which the public may lawfully abate. The owners hold the land under the water subject to the public right of passage over it. The proprietors of adjoining banks are entitled to use the water of the river, and the land under it, as regards the public, in any manner or for any purpose whatever, not inconsistent with this easement; and neither the state nor any private individual has a right to alter the course or character of the stream, or to render it by any means less useful to the owner of the soil. - When a piece of land in a conveyance lies upon and is bounded by a navigable pond of water, it is generally held that the grant only extends to the margin of the pond, and the grantee acquires no right to the soil beneath it. So riparian owners on technically navigable rivers, that is, on rivers in which the tide flows, are not entitled, as a matter of right, to the soil under the water in front of their uplands, because it belongs to the state.

The land covered by navigable ponds and lakes also belongs to the state when these are not private property, but a grant of the bed of such a pond or lake could only be made to the owner of the adjoining shore. - If the water running between the lands of separate owners gains gradually and imperceptibly upon one side or the other, the title of each continues as before to the middle of the stream regardless of the change. But if the change takes place suddenly and visibly, the ownership remains unchanged, and the boundary line continues as previous to the alteration, at what then was the middle of the stream. If therefore the river should suddenly and entirely forsake its natural channel, and make for itself a new one in the lands of the proprietor on one side, he would thereby become the exclusive owner of the soil under the whole river so far as it was enclosed in his land. If soil be formed by alluvium or the washing up of earth out of the river, by slow and imperceptible accretion, or by the dereliction of waters which have gradually receded and left the land beneath them bare and dry, it belongs to the owner of the adjoining land. Islands formed in the same manner are subject to the same rule.

If they are formed near the shore, they belong to the person who owns the land on that side of the stream to which they are nearest; if they are formed in the middle of the stream on both sides of the dividing line or centre, they belong to the proprietors on both sides in proportion to the extent which may lie on their respective sides of the line. Lands and islands formed out of the sea, or in navigable, i. e., tide rivers, belong to the sovereign or state, and not to the proprietors of the adjoining shore. By the common law the seashore, being that part between high and low water mark where the tide ebbs and flows, belonged to the sovereign or state, and was common to all the public, the possession of the adjoining proprietors extending only to high-water mark; but in this respect the common law has been changed in Massachusetts and Maine, as to owners on bays and arms of the sea, by the colony ordinance of 1641 and the usage arising therefrom, and the proprietorship goes to low-water mark, subject to the public easement and not exceeding 100 rods below high-water mark.

And now, in other states which lie on tide waters, the owner of land has some right to use it as far as low water, for the purpose of putting a wharf or similar building there. - The common law definition of a navigable river, being one where the tide ebbs and flows, has been considered and judicially adjudged to he inapplicable to the great rivers of Pennsylvania, Alabama, and other states. These rivers are declared to be navigable, and the boundaries of adjacent lands extend not to the middle of the stream, but only to low-water mark. But this question, where not particularly regulated in the several states by statute or judicial decisions, is still somewhat unsettled; and even where navigable waters are declared to be common highways, and as such for ever free to the public, it does not appear that the common law principle, that he who owns the land on both sides owns the entire river, and he who owns the land on one side only owns to the middle of the river, in both cases subject only to the easement of navigation, is thereby abolished. - While every riparian proprietor has an equal right to the free use of the water which passes his land, as it is accustomed to flow, without any diminution or alteration as to quantity or quality, he has no exclusive property in the water itself, but a simple usufruct while it passes along; and he cannot appropriate it to his exclusive use, or divert it from its natural channel, without the consent of the adjoining proprietors, who have an equal right to its use with himself.

If he does divert it on his own premises, he must return it to its ordinary course when it leaves his estate. He may use it to irrigate his lands or to water his cattle, or he may use the whole force of it in any reasonable manner he chooses, so long as such use does not interfere with the rights of his neighbors. But he cannot use it to the prejudice of any adjoining proprietor, unless he has a prior right to divert it, or a right by grant or by prescription (which supposes a grant) to some exclusive enjoyment of it. Whether, without such right, his use is reasonable, depends upon the circumstances of each case. The natural title which riparian owners thus have to the reasonable use of the waters may be restricted, altered, or enlarged by such grants or prescriptions; otherwise streams of running water could never be effectually applied either to agricultural or manufacturing purposes. Twenty years' exclusive occupation and use of water in any particular manner raises the presumption of a grant for that purpose from the adjoining proprietors; and owners whose land lies above or below must take the stream subject to such adverse right.

But nothing short of an express grant, or the use and enjoyment of the water so diverted or obstructed, or materially changed in its course and character, for a sufficient length of time to raise the legal prescription of a grant, will justify the owner as against any other owner to whom such alterations may prove injurious. - By the common law the proprietor of land lying upon an unnavigable river possesses the exclusive right to fish therein, as far as the middle of the stream; and if he owns both sides he has exclusive right, for fishing purposes, to the whole river, as far as his land extends, subject only to the rights of the public in the same as a highway for navigation. But this right is qualified by the same general rule which regulates his other riparian rights; it must be so used as not to injure or interfere with the rights and privileges of others. Therefore he cannot erect dams, weirs, or other obstructions for the purpose of preventing the ascent or passage of fish. Such impediments were regarded by the common law as a nuisance, and in Massachusetts the party offending in this manner is subject to a penalty provided by statute.

The common law right of fishing may be controlled or modified by the municipal law of the land, and in many of the states it is regulated by statute provisions. On navigable rivers and tide waters, however, the adjoining proprietors do not possess this exclusive right of fishing opposite to their own lands; it is a public and common privilege in which every one is equally entitled to share. But this public right of fishing in the water does not extend to permitting a stranger to pass over the land of another in order to reach the water. Neither are persons claiming and enjoying this common right entitled to draw the seine, or to fish, or build fishing huts, or dry their nets, upon the land of the adjoining owner, or upon islands which are private property; this privilege belongs exclusively to the owner of the soil. The civil law declared that the right of fishing was common in rivers, as well as in the sea, and gave the use of the adjoining banks for this purpose to the public. This principle is acknowledged where the civil law prevails, and has been adopted by some of the states in regard to their large navigable rivers, but it is unknown to the common law.

A question which has been much discussed and variously regulated by different nations is that relating to the public right to a foot or tow-path along the banks of navigable rivers, and the use of the banks for the assistance or convenience of navigation. The civil law allowed such a right, and held that all persons had the same right to bring their vessels to land and fasten ropes to the banks of the river that they had to navigate the river itself. The same doctrine is held in Louisiana, where it has been decided that, though the banks of navigable rivers are the property of those who own the adjoining lands, yet they are so far subject to the public use, that vessels may make fast to the shore and to the trees upon it, and may unload and deposit their goods there. The rule in Illinois, Tennessee, and Missouri seems to be substantially the same. In New York, Delaware, Pennsylvania, Michigan, Mississippi, Indiana, and perhaps some other states, it has been adjudged that the public have no such right as against the will of the owner.

The common law, according to Bracton, was anciently the same as the civil law, but the point remained unsettled till 1789, when it was decided that there was not any right at common law for the public to tow on the banks of navigable rivers. - Another unsettled question in the United States is that respecting the right of ferriage which attaches to riparian ownership. This matter is generally regulated by statute, and the state, by virtue of the law of eminent domain, claims the right to establish ferries wherever the legislature may consider them necessary for the public accommodation, regardless of the ownership of the soil, except as giving a claim for just compensation. But the statutes usually authorize the grant of the franchise by way of preference to the owners of the land on each side of the river where the ferry is established. It has been held that the riparian owner has not, as a matter of right, the privilege of keeping a ferry, and that it can only arise from a grant, actual or implied. This was probably the rule of the common law.

But, in the United States, we should say that it is the prevailing rule that the right to a ferry attaches to the riparian proprietor; that it cannot be taken from him without compensation; that he may convey the soil excepting the right of ferriage, which then becomes an incorporeal hereditament, and may be granted in the same way as a rent; and the grantee will have a right to use the adjoining soil so far as may be necessary for ferry ways, but not otherwise.