Do a Google search to familiarize yourself with what government agencies have management responsibilities for Lake Havasu. I just did it, & saw what counties surround the Lake, plus see Arizona has Lake Havasu State Park there, & the US Bureau of Reclamation is very involved with the lake, etc. Each of the counties has a marine patrol division that's active on it.
Today's News-Herald - Serving Lake Havasu City & The Lower Colorado River Area
I know you're new & very excited to get your scanner going, but it's very rewarding as well as respectable to do research on your own, then ask some questions of others here.
Obviously this is the off-season, but I'd on-season, I'd monitor:
AZ State Parks
Bureau of Reclamation
Mohave SO
SBSO Marine Div talk groups
Lake Havasu City PD
All US VHF Marine channels, especially 16 & those reserved for LE use.
FRS radio channels
Looks like all the rental houseboats come with a VHF marine radio, & I can imagine there's a lot of screwing-around on the radios by some, whereas others never bother to even monitor the radio, and small boats not having a radio at all.
My *guess* is that the couple of different public safety agencies that patrol the lake will coordinate with each other on a discrete VHF marine channel, plus monitor VHF 16, and have their own public safety radio system radios.
Have you done an FCC database search yet for licenses in the vicinity of Lake Havasu?
Figure out how to do a GeoSearch on this web page:
License Search - Advanced License Search
Many episodes of a 'reality' show on the Tru TV Channel showed LE ops during the height of Lake Havasu's wild season a year or two ago. You can watch the old episodes to gather intel on LE radio comms:
Party Heat on truTV
Please don't grow up to be a fat, greasy scanner-geek! When out on Lake Havasu during the Summer, put the radio away & go chase some booty.