Grant,
I just wrote a lengthy answer to this, but lost it when I went to post it. Here's the short version...
Contrary to popular belief "joe average fisherman" isn't considered a "vessel engaged in fishing" under the International Maritime Organization's Collision Regulations.
http://www.boatsafe.com/nauticalknowhow/boating/colregs.html Rule 3d states, "The term 'vessel engaged in fishing' means any vessel fishing with nets, lines, trawls, or other fishing apparatus which restrict maneuverability, but does not include a vessel fishing with trolling lines or other fishing apparatus which do not restrict manageability."
-> Therefore, your average guy fishing on a lake is considered a powder-driven vessel (PDV) under the rules, and therefore isn't given an "special" consideration because he is "fishing".
As for lights...
Rules 20 - 30 cover it, but basically the shall be exhibited from sunset to sunrise, during periods of restricted visibility, and at any other time deemed appropriate.
In his case, for a PDV less than 50m, he should display one all-round white light as he is at anchor.
If a vessel is "underway", as defined in Rule 3i,(ie not at anchor, or made fast to the shore, or aground) it shall exhibit lights as per Rule 23a or c. Ie. running lights in addition to an all-round white light for vessels <12m.
-> Note that by this definition, you are considered "underway" even if you are drifting.
Hopefully this helps shed some light on the subject! ;)
Cheers