I would. Although you are in fresh water, any chance of the wiring getting damp will tend to result in corrosion.
Some of the residential speaker wire - the clear plastic stuff - has marginal insulation, especially the cheap "made in China" stuff, and can wick moisture into the copper.
Also, Ancor speaker wire (which I used in my boat) is tinned on both leads, while the typical speaker wire used for the home has one wire tinned and one wire bare copper. Tinned wire has superior corrosion resistance.
Here is a very interesting and great article on speaker wire (probably more than you want to know):http://www.roger-russell.com/wire/wire.htm
Pay particular attention to the section: "All low cost wires are not the same" with reference to inferior cheap speaker wire that you can buy at Home Depot and Lowes (the made in China type stuff).
In a damp environment, the chance of corrosion will also depend somewhat on the terminals you use. Anytime dissimilar metals are in contact with each other and get wet, you'll get corrosion.
Read Roger's take on using gold-plated connectors. What I like to do is use tinned wire. If the connectors on the amp (or other device you are connecting to) are gold plated, then I use gold plated terminals on the wire. And I use connectors that have heat shrink adhesive on their shanks so that the gold-tin joint is sealed with heat shrink. This (hopefully) protects the gold-tin joint from moisture.
If the amp has tin-plated connectors, then I simply use tin-plated terminals. In this situation, there is really no need to use the more expensive heat shrink connectors.
There is less potential for corrosion in fresh water, but there is still a potential.
So unless you know you are using high-quality wire, why not use marine-grade wire, especially if you only need a few feet.
I bought mine at www.genuinedealz.com
, but it appears they no longer carry the Ancor speaker wire, so google on Ancor Speaker Wire and find your best price.