There are a # of trout water temp ,DO and aeration threads here. While the surface should be cooler the question that often comes up is if the water temp overall will stay low enough and have enough O2 to let the trout survive. Here are a couple links.

Here is some info from prior threads wrt wells/aeration and trout/ summer temps.

Horizontal aeration

http://www.pondboss.com/cgi-bin/ubbcgi/ultimatebb.cgi?ubb=get_topic;f=11;t=000125

Trout Success in 2006!

http://www.pondboss.com/cgi-bin/ubbcgi/ultimatebb.cgi?ubb=get_topic;f=20;t=003522;p=1

Trout Summer Survival

http://www.pondboss.com/cgi-bin/ubbcgi/ultimatebb.cgi?ubb=get_topic;f=20;t=003024