(From Iowa Legislature’s Administrative Rules Review Committee Digest)
Animal feeding operations: major water source, IAB Vol. XXVIII, No. 10, ARC 4652B, NOTICE.
The EPC proposes to update its list of streams and rivers that constitute a “major water source”; this term is defined in §459.102(33) as: “a water … capable of supporting a floating vessel capable of carrying one or more persons during a total of a six–month period in one out of ten years, excluding periods of flooding…” Note this is a broad definition, taking into account the recreational use of the waters; some states retain a narrower view of navigation, limiting it to commercial uses.
Inclusion on this list is significant. §459.310, Iowa Code requires a 1,000 foot separation distance between a confined feeding operation and major water source, while only a 500 foot separation is required for smaller water resources.

For that reason it is important that the resources be accurately designated. Each individual segment of these streams has not been examined. Instead, a formula has been used. A perennial stream, one that has a water flow all year is designated a first order stream. A second-order stream is fed by at least two first-order streams. The joining of two-second order streams forms a third-order stream. Stream ranking continues until the highest-ordered channel is reached. The Amazon is a twelfth order stream.

First and second-order streams typically carry small volumes of water. The EPC believes that a forth [sic] order stream meets the definition of a “major water source” as being able to support a floating vessel. The stream segments added by this rulemaking were designated because they meet the definition of a forth order stream; i.e. thee confluence of two third order streams.