Who Owns Islands in Montana Rivers

Montana Code Annotated 70-18-2 Watercourses


Rivers, streams, and creeks are an important – maybe the lifeblood – of Montana’s geography, economy and culture. Access to these rivers and the water therein are a key part of our economy and culture. However, because rivers change course and laws and politics change, confusion often exists about ownership and access to these rivers.

Our Stream Access Law provides for recreational access to the high water mark. But this is recreational access only – not ownership. The public only owns the bed of large non-navigable rivers. Furthermore, the SAL does not provide for access to islands above the high water mark, which may or not be owned by the public.

The following is a brief discussion of some of the law and regulations involved with island ownership. It is not intended as legal advice. Consult an attorney if you intend to take any legal action.

The FIRST STEP in determination of island ownership is to determine if the river is
non-navigable or navigable.


All rivers other than those listed in section III below are non-navigable. Generally the smaller rivers. On non-navigable rivers, private property lines go to the middle of the river and island ownership is thus determined by property deeds. The following statute applies to islands on non-navigable rivers:

MCA (Montana Code Annotated) 70-18-204. Islands formed in non-navigable stream. An island or accumulation of land formed in a stream which is not navigable belongs to the owner of the shore on that side where the island or accumulation is formed or, if not formed on one side only, to the owners of the shore on the two sides, divided by an imaginary line drawn through the middle of the river.

III. NAVIGABLE RIVERS (This is where the fun starts.)

NAVIGABLE RIVERS DEFINED: The Montana Department of Natural Resources and Conservation defines navigable rivers as any streambeds that have a history of commercial use or navigation, and claims ownership to the beds of these rivers. For purposes of the stream access law a different definition applies.

They have been researched and are specifically enumerated in 2008 DNRC regs as: the Big Hole, Big Horn, Bitterroot, Blackfoot, Boulder (Yellowstone drainage), Bull River, Clark Fork, Clearwater, Dearborn, Dupuyer Creek, Flathead River including Middle, North, and South forks, Fortine Creek, Gallatin river, Graves Creek, Jefferson, Kootenai, Lolo Creek, Madison, Marias, Milk, Missouri, Nine Mile Creek, Rock Creek (Yellowstone Drainage), Sheep Creek, Smith River, Stillwater River (Flathead drainage), Sun River, Swan, Teton, Tobacco, Tongue, Whitefish, Yaak, and Yellowstone. The smaller streams or rivers on the state list may or may not be recognized as navigable by the Federal agencies. They recognize navigability only if it has gone to federal court and so adjudicated.


Unless patented (deeded) to private parties, islands within meander survey lines of rivers surveyed by the Government Land Office (G.L.O.) are owned by the Federal government, administered by the Bureau of Land Management, and accessible to the public. The original surveys done around the turn of the last century by the GLO, and resurveys can be viewed on microfilm at the Billings Area BLM office. In addition “MASTER TITLE PLATS” showing known federal ownership in and around rivers can be viewed at the same office.

The BLM staff includes surveyors who can make ownership determinations based on surveys, aerial photography and other evidence (aerial photography done every 10 years documents changes in river channels). They do not do this routinely – only on a case-by-case basis as needed.


The state of Montana claims ownership of the beds of navigable rivers between the low water marks – not the high water marks. Any islands within these low water marks of navigable rivers, not deemed owned by the Federal government or private parties, are claimed by the State of Montana and accessible to the public.

DNRC is the state agency with responsibility for administration law in this regard. They do not have a data base of islands owned by the state and do not necessarily attempt to systematically determine island ownership in the beds of navigable rivers. Such work is handled on a case by case basis as the need arises. The DNRC staff specialist working with island ownership is a hydrogeologist in Helena.

Property boundaries around navigable rivers. Government survey offices and DNRC advise that property boundaries along rivers go to the low water mark (even though the stream access law gives recreational access rights to the high water mark).

The following Montana Code (MCA) statutes apply:

77-1-102. Ownership of certain islands and riverbeds. (1) The following lands belong to the state of Montana to be held in trust for the benefit of the public schools of the state:

(a) all islands existing in the navigable streams or lakes in this state that have not been surveyed by the government of the United States; and

(b) all lands that at any time in the past constituted an island or part of an island in a navigable stream or lake.

(2) This section does not apply to lands that are occupied by and belong to riparian landowners if the lands were formed by accretions.

(3) State-owned riverbeds are public lands of the state that are held in trust for the people as provided in Article X, section 11, of the Montana constitution.

70-18-203. Islands formed in navigable stream. Islands and accumulations of land formed in the beds of streams which are navigable belong to the state if there is no title or prescription to the contrary.

Note: This includes islands formed by “vertical” accretion which attach to a private property. The “cow test” applies. This test says that if vegetation suitable for grazing appears on land formed by vertical accretion, the land is an island.

70-18-201. Alluvion or accretion – increase of bank. Where from natural causes land forms by imperceptible degrees upon the bank of a river or stream, navigable or not navigable, either by accumulation of material or by the recession of the stream, such land belongs to the owner of the bank, subject to any existing right-of-way over the bank.

(Alluvion or accretion is the gradual increase in land on a river bank caused by flood or current. In accordance with the above statute such land belongs to the owner of the bank. However, if such accretion merely fills in an old channel and creates the apparent attachment of an island to the bank, such an island may or may not belong to the owner of the bank. If, as was the case for the “Bundy Bridge” island, such an island is publicly owned, the apparent attachment to the bank does not create ownership of that island by the owner of the bank.)

70-18-205. Island formed by division of stream. If a stream, navigable or not navigable, in forming itself a new arm, divides itself and surrounds land belonging to the owner of the shore and thereby forms an island, the island belongs to such owner.

In addition to the statutes noted above there is a significant body of case law applicable to island ownership.

IV How to check out an island in a navigable river.

Sorry, there is no cookie cutter check list. You may have to dig around a lot. The first thing to do in the case of navigable rivers is to check the BLM maps. You may find the island clearly identified as publicly owned.

If not identified as publicly owned, and you still think it might be, check GLO surveys at the BLM office and property deeds at the court house. Then check with staffers at BLM and/or DNRC to see if they know anything about the islands. You may find out it is clearly private or clearly public.

If still unknown, you may need to get a surveyor or land specialist involved – either one you hire or one from a government agency. They will research public records and do the physical survey as necessary. If the research and survey info is on your side, an attorney (either yours or from an agency) would have to take appropriate legal action if a private party is asserting ownership.

Doing all this on your own can be very expensive and time consuming. The more help you can get from agency staffs, the better. However, you will probably always have to do much of the initial “grunt work” either way.

Property tax status – One – and only one – of the determinants of whether or not an island is public or private is whether or not anyone is paying taxes on it. Landowners who assert island ownership often are not paying taxes on them. The Montana Department of Revenue is the source for this information. They have offices in every county complete with maps showing ownership for tax purposes.

Contacts and Information Sources

DNRC Minerals Management Branch Chief – Helena 444-3843
DNRC Helena – Hydro-geologist – 444-2845
Billings BLM – Lands Adjudication – 896-5044
Billings BLM Survey office – 896-5132
Surveyor Billings Area BLM office .
DNRC Billings office – 247 -4404

* CAVEAT – Islands and streambeds inside of Indian reservations have an additional layer of applicable law not researched for this effort.

Public Land/Water Access Association Inc. or PLWA,
is a citizen group organized and operated under the Montana nonprofit corporation act.
The Internal Revenue Service has made a determination that PLWA qualifies as a tax- exempt
organization under Section 501(c)(3) of the Internal Revenue Code and that it is a public charity.

Articles and Information on this site represent the opinion of the writer and are not intended as legal advice.
Legal counsel may be needed in dealing with specific access situations and issues.