I kayak fish and learned a long time ago not to wear shorts in the yak, my legs and thighs got burned during a "quick" trip on a local river.
Could barely walk at work for a couple of days.
Long sleeve shirts, long pants, light poly socks, hat and sun screen for the neck and ears.
Also use the stick sunscreen for the face and schnozz.
I have a bunch of tech shirts that they gave out at Kayak fishing tournaments.
One thing to be aware of with those if the weather turns while out; clouds, rain and wind, they can get really cold fast.
I was out a couple of weeks ago when that happened to me, luckily I was only a mile from the launch but by the time I got there I could feel the beginning of hypothermia coming on.
Always carry a spare cotton shirt in a dry bag and towels in the car.