Definition
A slough is an arm or branch of a river that flows between islands and the mainland, separating those islands from one another. A slough is distinguished from the main channel by two characteristics: it is narrower than the main river, and the primary body of the river's water does not flow through it. Sloughs are secondary watercourses that branch off from and typically reconnect with the main stream, carrying water at reduced volume and velocity.
Bouvier's Law Dictionary records a second, archaic English usage: "Slough Silver," a customary rent paid in lieu of harvest labor owed to the castle of Wigmore, England. This feudal rent meaning has no modern legal application and appears only in historical English property records.
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Common Language
Modern common usage (Wiktionary): To shed skin or an outer layer; to slide or flake off; to discard; informally, to be truant or absent from school without permission.
Historical common usage (Webster's 1913): Defined as an archaic form of "slow," attributed to Chaucer.
Neither the modern common meaning (shedding or discarding) nor the historical common meaning (slow) bears any relationship to the legal meaning. In law, SLOUGH is exclusively a term of geography and property, identifying a specific type of secondary watercourse. A researcher encountering the term in deeds, survey plats, water rights disputes, or boundary descriptions should not import any meaning from the common verb form.
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Common Confusion
The spelling "slough" covers at least two distinct words in ordinary English — the verb meaning to shed (rhyming with "stuff") and the noun meaning a swamp or marshy inlet (rhyming with "blue" or "plow," depending on dialect). The legal meaning aligns with the noun form but is more precise than the common noun: a slough in law is specifically a branch of a river between islands and mainland, not simply any marsh or boggy depression. Courts applying this definition have required the watercourse to meet the structural criteria — secondary channel, reduced flow, connection to a main river — rather than treating any wet or marshy area as a slough.
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Why It Matters in Research
SLOUGH is primarily a term of art in water law, property boundary disputes, and public land surveys, particularly in states with river systems that produce complex channel networks — the Mississippi, Missouri, and Iowa river corridors produced much of the early American case law on the term. Researchers should note several navigational considerations:
**Boundary and title research.** Property descriptions in deeds and government survey plats from the 19th and early 20th centuries frequently use slough as a natural monument or boundary marker. Where a slough has since dried up, silted in, shifted, or been channelized, establishing what the original boundary meant requires reconstructing the historical watercourse. This is a common source of title disputes in river-adjacent land.
**Water rights and navigability.** Whether a slough qualifies as a navigable waterway affects questions of riparian ownership, public access, and state versus private title to the bed. Because sloughs carry less of the main stream's flow and are narrower than the principal channel, courts have sometimes found them non-navigable even where the main river is navigable. The distinction matters for whether the adjacent landowner holds title to the bed.
**Reclamation and drainage law.** In jurisdictions that undertook major drainage and reclamation projects in the late 19th and early 20th centuries, sloughs were frequently drained, filled, or incorporated into drainage districts. Legal records from those projects may use slough in ways that assume local custom rather than the technical definition.
**Bouvier's "Slough Silver" entry.** This feudal rent term will almost never appear in American legal research contexts. Researchers encountering it in English legal history or manorial records should treat it as wholly unrelated to the watercourse meaning.
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Historical Dictionary Support
Black's (1st Ed.) and Black's (2nd Ed.) are substantively identical on this term, both deriving their definition from the same Iowa case involving the Dunleith & Dubuque Bridge Company. This suggests the legal definition was not a subject of broad common law development but was crystallized relatively early from a narrow set of cases. Black's 2nd Ed. adds the full citation (Dunleith & D. Bridge Co. v. Dubuque County, 55 Iowa 565, 8 N.W. 443), which is a genuine Iowa Supreme Court case from 1881.
Bouvier adds the "Slough Silver" note, which Black's omits entirely — the sole point of divergence between the dictionaries. Bouvier treats it as a historical English curiosity, and it is noted without elaboration in either edition of Black's because it had no American relevance.
None of the historical dictionaries address the navigability question, the public land survey context, or drainage law implications — all areas where the term has generated significant litigation. Researchers relying solely on historical dictionary definitions will have the geographical structure of the term but will miss the legal consequences that flow from classification as a slough.
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Jurisdictional Note
The legal definition is most developed in Midwestern states with major river systems, particularly Iowa, where the controlling case originated. Western states with complex river delta systems — California's Sacramento-San Joaquin Delta, for example — use "slough" extensively in both statutes and property records, sometimes with local meaning that emphasizes tidal influence. Researchers working in California water law or property records should verify whether local usage tracks the Black's definition or reflects a broader marsh/inlet meaning.
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