Where exactly is the Idaho-Oregon and Idaho-Washington border on the Snake River, and how far do Idaho's police, courts, and civil laws reach across the water?

Plain-English summary

The Nez Perce County prosecutor asked a basic but tricky question: when the Snake River forms the line between Idaho and Oregon (or Idaho and Washington), where exactly is the line, and how does that determine which state's laws govern any given activity on the water?

The AG's answer drew on a long line of U.S. Supreme Court cases. When a navigable river forms a state boundary, the boundary is the middle of the main navigable channel, also known as the "thalweg." The rule was first applied to interstate boundaries in Iowa v. Illinois (1893) and reaffirmed in cases like Louisiana v. Mississippi (1906 and again in 1984). The U.S. Supreme Court applied it specifically to Idaho in Scott v. Lattig (1913), and the Ninth Circuit confirmed it in 1983.

Idaho's Constitution, the Organic Act, and the Admission Bill all describe the boundary using the words "channel," "mid-channel," or "thread of the stream," but those phrases all point to the same legal concept: the middle of the main navigable channel. The thalweg is not a fixed line drawn on a map. It can shift over time with erosion and accretion, and it must be located on the ground by examining the course commonly taken by vessels navigating that reach of the river. So determining the precise physical boundary at any point of interest is a case-by-case factual question.

What flowed from the boundary location was the AG's main point: Idaho's full civil and criminal jurisdiction reached every activity on the Idaho side of the live thalweg, with one narrow carve-out. The Idaho legislature had authorized limited reciprocal arrangements with Oregon and Washington under Idaho Code § 36-1001, but only for hunting, fishing, and trapping in the waters or on the islands of the Snake River. Outside that narrow category, the legislature had not compromised state jurisdiction. Persons engaged in any other activity (criminal acts, civil disputes, regulated business activity) on the Idaho side of the thalweg were subject to Idaho law.

Currency note

This opinion was issued in 1988. Subsequent statutory amendments, court decisions, or later AG opinions may have changed the analysis. Treat this page as historical context, not current legal advice. Verify current law before relying on any specific rule, deadline, or remedy mentioned here.

Background and statutory framework

The Tenth Amendment reserves to the states all powers not delegated to the federal government. Among those reserved powers is the authority to enact a civil and criminal code and enforce it against people within state territorial jurisdiction. Only a state legislature can yield that sovereignty, and a court will not assume relinquishment.

Idaho's territorial border is set out in art. XVII, § 1 of the Idaho Constitution and in the matching language of the federal Organic Act of the Territory of Idaho and the Idaho Admission Bill. All three describe the Snake River segment as running through the "middle channel" or "mid-channel" of the Snake. The case law translating that geographic phrase into a legal rule is the thalweg doctrine. The U.S. Supreme Court grounded the rule in the policy of preserving each state's equal access to navigation: drawing the line at the middle of the main navigable channel ensures both states have the same right of use.

In Scott v. Lattig, the U.S. Supreme Court explained that on Idaho's admission to statehood, the bed of the Snake River on the Idaho side of the "thread of the stream" passed from the United States to Idaho. The opinion uses "thread" interchangeably with "thalweg" or "middle channel." Louisiana v. Mississippi added the practical refinement that the live thalweg can shift gradually with erosion and accretion, and that its location is determined by where vessels actually navigate.

To handle the practical headaches of cross-border activity, Idaho's legislature had enacted Idaho Code § 36-1001 et seq. authorizing reciprocal hunting, fishing, and trapping arrangements with the neighboring states. The AG read those statutes narrowly: they did not authorize broader yields of jurisdiction.

Common questions

Where is the Idaho-Oregon or Idaho-Washington line in the Snake River?

It runs through the middle of the main navigable channel, the "thalweg." Idaho's Constitution, the Organic Act, and the Admission Bill all use language ("middle channel," "mid-channel," "thread") that the U.S. Supreme Court has consistently interpreted to mean the thalweg.

Does the line move?

Yes, the live thalweg can shift over time with the gradual processes of erosion and accretion. The U.S. Supreme Court recognized this in Louisiana v. Mississippi. To pin down the actual location at a particular point, a court considers where vessels customarily navigate that reach.

Did Idaho law reach activities on the Idaho side of the thalweg in 1988?

The AG concluded yes. Subject to one narrow exception, Idaho's full civil and criminal jurisdiction reached every activity occurring on the Idaho side of the main navigable channel. The state could enforce its criminal code, regulate business, adjudicate civil disputes, and apply its rules to persons or entities operating there.

What was the exception?

Idaho Code § 36-1001 et seq. authorized reciprocal arrangements with Oregon and Washington for hunting, fishing, and trapping in the waters or on the islands of the Snake River. Outside that narrow category, the legislature had not yielded jurisdiction. The AG was clear that jurisdiction is yielded only by an explicit legislative act, never by assumption.

Why does the rule come from a 19th-century Supreme Court case?

The thalweg doctrine traces to Iowa v. Illinois (1893) and earlier admiralty doctrine. The Court returned to it repeatedly when deciding original-jurisdiction interstate boundary disputes. The 1988 opinion treated the rule as well-settled and applicable to Idaho's Snake River boundary specifically through Scott v. Lattig (1913) and Grand Canyon Dories (9th Cir. 1983).

Citations

Constitutions: U.S. Const. amend. X; Idaho Const. art. XVII, § 1.

Federal statutes: Organic Act of the Territory of Idaho, ch. 117, 12 Stat. 808; Idaho Admission Bill, ch. 656, 26 Stat. 215.

Idaho statutes: Idaho Code § 36-1001 et seq. (Supp. 1988).

Federal cases: Alfred L. Snapp and Son, Inc. v. Puerto Rico, 458 U.S. 592 (1982); Arkansas v. Mississippi, 250 U.S. 39 (1919); Grand Canyon Dories, Inc. v. Idaho Outfitters and Guides Board, 709 F.2d 1250 (9th Cir. 1983); Iowa v. Illinois, 147 U.S. 1 (1893); Louisiana v. Mississippi, 202 U.S. 1 (1906); Louisiana v. Mississippi, 466 U.S. 96 (1984); Scott v. Lattig, 227 U.S. 229 (1913); United States v. Brown, 552 F.2d 817 (8th Cir. 1977), cert. denied, 431 U.S. 949 (1977); Washington v. Oregon, 211 U.S. 127 (1908), aff'd on rehearing, 214 U.S. 205 (1909).

State cases: Smith v. State, 64 Wash. 2d 323, 391 P.2d 718 (1964).

Source

• Landing page: https://www.ag.idaho.gov/office-resources/opinions/
• Original PDF: https://ag.idaho.gov/content/uploads/2018/04/OP88-07.pdf

Original opinion text

STATE OF IDAHO
OFFICE OF THE ATTORNEY GENERAL
JIM JONES
ATTORNEY GENERAL

BOISE 83720

TELEPHONE
(208) 334-2400

ATTORNEY GENERAL OPINION NO. 88-7

TO: Steve J. Tobiason
Prosecuting Attorney
Nez Perce County
P.O. Box 1267
Lewiston, ID 83501

Per Request for Attorney General's Opinion

QUESTION PRESENTED:

When the boundary of the state of Idaho is defined in part by the Snake River, what is the extent of Idaho's civil and criminal jurisdiction over activities occurring on the river?

CONCLUSION:

When the boundary of the state of Idaho is defined in part by the Snake River, that boundary is located in the middle of the main navigable channel of the river. Idaho's full civil and criminal jurisdiction extends to all activities occurring on the Idaho side of the main navigable channel unless the Idaho legislature has specifically provided otherwise.

ANALYSIS:

You have asked this office to advise you on the extent of Idaho's civil and criminal jurisdiction over activities occurring on the Snake River. Under the tenth amendment to the United States Constitution, powers not delegated to the United States by the Constitution, or otherwise prohibited by it to the states, are reserved to the states. Among the sovereign powers reserved to the states is the power to create a legal code, both civil and criminal, and to enforce that code against individuals and entities within the territorial jurisdiction of each respective state. Alfred L. Snapp and Son, Inc. v. Puerto Rico, 458 U.S. 592, 601, 102 S.Ct. 3260, 3265, 73 L.Ed.2d 995, 1003 (1982). Only a legislature can yield a state's sovereign powers. Smith v. State, 64 Wash. 2d 323, 330, 391 P.2d 718, 723 (1964). Further, it cannot be assumed that a state has relinquished its sovereignty. United States v. Brown, 552 F.2d 817, 820 (8th Cir. 1977), cert. denied, 431 U.S. 949, 97 S.Ct. 2666, 53 L.Ed.2d 266 (1977).

Because Idaho's jurisdiction depends upon whether activities occur within the territorial limits of the state, consideration must first be given to understanding the nature of a boundary delineated by an interstate navigable river.

The Snake River marks part of the boundary between the state of Idaho and the states of Washington and Oregon. As described in art. XVII, § 1 of the Idaho Constitution, the boundary formed by the Snake River runs as follows:

Beginning at a point in the middle channel of the Snake river where the northern boundary of Oregon intersects the same; then follow down the channel of Snake river to a point opposite the mouth of the Kooskooskia or Clearwater river . . . .

The Organic Act of the Territory of Idaho, ch. 117, 12 Stat. 808, contains identical language. Similarly, the Idaho Admission Bill, ch. 656, 26 Stat. 215, describes the boundary as, "thence down the mid-channel of the Snake River to the mouth of the Clearwater River . . . ."

The territorial boundary of Idaho marked by the Snake River has been addressed by the courts. In the early case of Scott v. Lattig, 227 U.S. 229, 33 S.Ct. 242, 57 L.Ed. 490 (1913), the U.S. Supreme Court noted:

Bearing in mind, then, that [the] Snake river is a navigable stream, it is apparent, first, that on the admission of Idaho to statehood the ownership of the bed of the river on the Idaho side of the thread of the stream — the thread being the true boundary of the state — passed from the United States to the state . . . .

227 U.S. at 243, 33 S.Ct. at 244, 57 L.Ed. at 496. More recently, the Court of Appeals for the Ninth Circuit stated that the Idaho boundary is located "in the middle channel of the Snake River." Grand Canyon Dories, Inc. v. Idaho Outfitters and Guides Board, 709 F.2d 1250, 1251 (9th Cir. 1983).

Although the boundary in question has been variously described as located at "the middle channel of the Snake river," "the mid-channel of the Snake River," and the "thread" of the river, it is well settled that where a boundary between states is marked by a navigable river, the boundary line is the middle of the main navigable channel of the river. Iowa v. Illinois, 147 U.S. 1, 8, 13 S.Ct. 239, 241, 37 L.Ed. 55, 57 (1893). See e.g., Louisiana v. Mississippi, 202 U.S. 1, 49, 26 S.Ct. 408, 421, 50 L.Ed. 913, 930 (1906); Washington v. Oregon, 211 U.S. 127, 134, 29 S.Ct. 47, 48, 53 L.Ed. 118, 119 (1908), aff'd on rehearing, 214 U.S. 205, 29 S.Ct. 631, 53 L.Ed. 969 (1909); Louisiana v. Mississippi, 466 U.S. 96, 99, 104 S.Ct. 1645, 1647, 80 L.Ed.2d 74, 78 (1984). This rule, known as the rule of the "thalweg," is based upon recognition of the importance of preserving to each state equality in navigation of a river. Arkansas v. Mississippi, 250 U.S. 39, 45, 39 S.Ct. 422, 424, 63 L.Ed. 832, 835 (1919).

Determining that the "live thalweg," or middle of the main navigable channel, is the legal boundary between states does not fix the location of the boundary physically or factually. As the U.S. Supreme Court acknowledged, a boundary defined as the "live thalweg" may vary from time to time, depending upon the course of the river as its bed and channel change due to the gradual processes of erosion and accretion. Louisiana v. Mississippi, 466 U.S. at 100-01, 104 S.Ct. at 1648, 80 L.Ed.2d at 78-79. Case law has established the proposition that the "live thalweg" is defined by the ordinary course of traffic on the river, i.e., by factually establishing the course commonly taken by vessels navigating a particular reach of a river. Id., at 101, 104 S.Ct. at 1648, 80 L.Ed.2d at 79. Thus, the actual physical boundary of the state of Idaho for a particular reach of the Snake River must be determined on a case-by-case basis after consideration of available evidence.

In recognition of the potential conflict, confusion and difficulties attendant to establishing the precise physical location of the state's boundary on the Snake River, the Idaho legislature has authorized certain limited reciprocal agreements with the states of Washington and Oregon. The reciprocal agreements authorized by the legislature extend only to the right to fish, hunt or trap in the waters or on the islands of the Snake River. See Idaho Code § 36-1001 et seq. The Idaho legislature has not otherwise acted to compromise its exclusive jurisdiction over other activities occurring on the Snake River within the territorial limits of the state. Consequently, persons or entities engaging in other activities on the Idaho side of the Snake River must comply with all applicable laws of the state of Idaho.

AUTHORITIES CONSIDERED:

Constitutions
United States Constitution, 10th Amendment.
Idaho Constitution, art. XVII, § 1.

Federal Statutes
The Organic Act of the Territory of Idaho, ch. 117, 12 Stat. 808.
Idaho Admission Bill, ch. 656, 26 Stat. 215.

Idaho Statutes
Idaho Code § 36-1001 et seq. (Supp. 1988).

Federal Cases
Alfred L. Snapp and Son, Inc. v. Puerto Rico, 458 U.S. 592, 601, 102 S.Ct. 3260, 3265, 73 L.Ed.2d 995, 1003 (1982).
Arkansas v. Mississippi, 250 U.S. 39, 45, 39 S.Ct. 422, 424, 63 L.Ed. 832, 835 (1919).
Grand Canyon Dories, Inc. v. Idaho Outfitters and Guides Board, 709 F.2d 1250, 1251 (9th Cir. 1983).
Iowa v. Illinois, 147 U.S. 1, 8, 13 S.Ct. 239, 241, 37 L.Ed. 55, 57 (1893).
Louisiana v. Mississippi, 202 U.S. 1, 49, 26 S.Ct. 408, 421, 50 L.Ed. 913, 930 (1906).
Louisiana v. Mississippi, 466 U.S. 96, 99-101, 104 S.Ct. 1645, 1647-48, 80 L.Ed.2d 74, 78-79 (1984).
Scott v. Lattig, 227 U.S. 229, 243, 33 S.Ct. 242, 244, 57 L.Ed. 490, 496 (1913).
United States v. Brown, 552 F.2d 817, 820 (8th Cir. 1977), cert. denied, 431 U.S. 949, 97 S.Ct. 2666, 53 L.Ed.2d 266 (1977).
Washington v. Oregon, 211 U.S. 127, 134, 29 S.Ct. 47, 48, 53 L.Ed. 118, 119 (1908), aff'd on rehearing, 214 U.S. 205, 29 S.Ct. 631, 53 L.Ed. 969 (1909).

Other Cases
Smith v. State, 64 Wash. 2d 323, 330, 391 P.2d 718, 723 (1964).

DATED this 5th day of December, 1988.

ATTORNEY GENERAL

ANALYSIS BY:
Steve Mendive
Merrilee Caldwell
Deputy Attorneys General
Natural Resources Division