Natural Springs should have warmed up to 3mm temps by August but that's above the thermocline (about 20 feet). Most of the quarry is 16-18 feet deep and in the summer the visibility is beyond dismal and the weeds have grown all the way to the surface so you almost need a machete to dive in some areas. (OK, you do need a machete.) There is a trench along the far side that drops to a little over 25 feet, it's colder but the visibility is better. You'll want a 5mm suit for the colder water and you'll probably want a hood and gloves if you plan to stay there any length of time.
Where on the east side of Indianapolis? I'm near Brookville, OH about 20 miles east of the Indiana/Ohio border. It takes me an hour and 45 minutes to get to Gilboa Quarry from the house. That's our premier site around here and would be worth the trip if you have a weekend available. If you're not too far from the Ohio border it would be a nice day trip as well but you're looking at over 2 hours of driving. Gilboa is best on the weekdays when there aren't any classes tilling the bottom. There are several Great Lakes Wrecking Crew people who are available on weekdays to dive, just post your intended dive date and location in the GLWC section and see who crops up! You'll want a 5mm suit at Gilboa but he does have some available to rent on site.
Ber :lilbunny: