Lets say I'm rafting in a river that marks the boundary between state A and B. While in said river I perform an action legal in state A but not in state B. I want to know if I broke the law.

How do I know which state's laws apply? Is it based on whether I am closer to one state's side of the river than the other? Do I have any defense for breaking breaking state B's law if I assumed I was still in state A's jurisdiction?

2 Answers 2


In most cases, the state boundary line controls.

For example, Kentucky owns the Ohio River along its border with Ohio, Indiana, and Illinois. In essence, the boundary between Kentucky and these three future states is the low point of the Ohio River's northernmost bank. This was established by a Congressionally passed law in 1792.

The boundary is defined by federal statute on a case by case basis for each of the rivers that is a boundary between U.S. states. Most codifications of a state's statutory laws also restate the federal statute defining the state's boundary at the beginning before the actual portion setting forth state laws begins.

In the case of the Rio Grande river, which is a boundary between the U.S. and Mexico, an international boundary treaty determines where the boundary between the U.S. and Mexico is for this purpose. International treaties similarly define all other international water boundaries of the United States.

This isn't the end of the story, however, because many activities that take place in the "navigable waters of the United States" (which basically means with respect to rivers, rivers wide and deep enough to be used for commercial transportation, like the Mississippi and Ohio Rivers and the Colorado River) are governed by federal admiralty law, rather than by state law (even if both sides of the river are in the same state).

For example, the employment law of ship crews operating on the navigable waters of the United States are governed by admiralty law, and so are most laws governing tort liability in collisions between boats/ships, and most laws governing salvage of boats/ships that have sunk.

Some admiralty law cases must be litigated in the U.S. District Courts (i.e. in the federal court system's trial courts) which have exclusive jurisdiction over some admiralty law issues, while other admiralty law issues, while still governed by federal admiralty law, may be litigated in either state or federal courts which have concurrent jurisdiction over some admiralty law issues.

Still, to the extent that admiralty law does not apply, the state law of the state in which that part of the river is located will govern.

Fun fact: As a young lawyer I once was part of a group of lawyers litigating an admiralty law case arising out of an incident taking place on the Colorado River near Grand Junction, Colorado.

Do I have any defense for breaking breaking state B's law if I assumed I was still in state A jurisdiction?

No. You could argue at trial that you really were in state A jurisdiction. But if the finder of fact at trial determines that you were in state B, then state B law applies.

  • 5
    While tangential to the OPs question, I'd also throw in "property rights" of land owners who have rivers flowing through their properties. I don't know about other states, but this was an issue in New Mexico that was only resolved last year
    – Peter M
    Commented Jan 31, 2023 at 23:17
  • 6
    There's a fun vocabulary word to throw around in this context: thalweg. Commented Feb 1, 2023 at 14:38
  • 4
    @MichaelSeifert Another good one is avulsion "The boundary between the states is the river. Not where the river is now, mind you, but where it was back before that one heavy rainstorm in 1973, at least for this one section."
    – R.M.
    Commented Feb 1, 2023 at 16:53
  • 1
    @hszmv Totally off topic here, but I was listening on NPR about cannabis dispensaries, and one of the financial issues with running one is that they can't claim expenses on federal tax returns - which really cuts into the profitability.
    – Peter M
    Commented Feb 1, 2023 at 17:56
  • 1
    @PeterM Yes. That section of the Internal Revenue Code is Section 280E. It has a huge impact on marijuana business law and I've dealt with tax audits related to it for clients.
    – ohwilleke
    Commented Feb 1, 2023 at 21:05

When rafting on a river boundary in the USA, you must abide by the laws of both states that the river runs through. The same laws can vary depending on the specific river and location, but generally, you must follow the rules and regulations for boating and recreational activities in both states. This can include rules for watercraft operation, fishing, camping, and other activities. If you are unsure of the specific laws for a particular river, it is best to check with local authorities or park rangers in both states. Additionally, it is always important to exercise caution and safety while rafting on any river, regardless of state laws.

  • 1
    Your answer could be improved with additional supporting information. Please edit to add further details, such as citations or documentation, so that others can confirm that your answer is correct. You can find more information on how to write good answers in the help center.
    – Community Bot
    Commented Feb 1, 2023 at 13:15
  • 2
    This is an incorrect statement of the law. It is almost never the case that the laws of more than one U.S. state will apply in a particular part of a river which is a boundary between U.S. states.
    – ohwilleke
    Commented Feb 2, 2023 at 1:26

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .