The Oxford Biblical Studies Online and Oxford Islamic Studies Online have retired. Content you previously purchased on Oxford Biblical Studies Online or Oxford Islamic Studies Online has now moved to Oxford Reference, Oxford Handbooks Online, Oxford Scholarship Online, or What Everyone Needs to Know®. For information on how to continue to view articles visit the subscriber services page.

Related Content

Related Overviews


More Like This

Show all results sharing this subject:

  • Law


Show Summary Details


rule of the thalweg

Quick Reference

[from German: literally, valley line]

The rule for determining the boundary line between two states that are separated by a navigable river containing a newly formed island. According to this rule, the boundary line moves with the centre of the navigable channel, i.e. it is delineated as being the centre of the course with the strongest current, so that the newly formed island must lie on one side of it or the other. In the case of Iowa v Illinois 147 US 7 (1893) the expression “middle of the Mississippi River” was interpreted as the “middle of the main channel” or “thread of the stream”. On non-navigable rivers, however, the middle line of the river will mark the boundary between the two states between which it flows. Thus, a newly formed island might well fall partly on one side of the boundary line and partly on the other. See also accretion; avulsion.

Subjects: Law

Reference entries