I wear a "doo-rag" I made out of Bug-Off brand handkerchief under my nylon/mesh baseball style fishing cap. If the sun isn't an issue, I just wear the doo-rag paddling and on portages.

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Protects ears/neck from sun/bug bites and can be dipped in lake to get a cooling effect.

I don't like to drink warm water but you have to stay hydrated so I use this simple trick.
If you using a standard size water bottle, take a old cotton tube sock and cut off the toe end.

Sleeve the bottle with sock and keep the sock wet and store bottle while paddling out of the direct sunlight.
The evaporation will cool your drink.
If you have bigger water containers, I have a couple of 1-2 litter Naglene Canteens and use a canvas bank coin sack secured with a Bungee/Bob around neck and do the same as I would with tube sock.

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This evaporation method allowed me to keep a LT I caught and cleaned on Jean lk, cool/fresh all the way down to Sturgeon lk and then to Scripture Island campsite on a day that was in the high 80's. Just keep the sock/bag wet and out of direct sun and your good to go.