You might also want to stop in Great Feathers (a couple of mile down York Road from Backwater Angler). Both shops will offer excellent advice on what's happening at the moment, but the advice may be different (between them they cover more of the river.)
Are you planning on going on a weekend or a weekday? Parts of the river get really crowded with float tubers on the weekend.
Any advice given today will probably be useless, because conditions vary considerably according to the how much water is being released from Pretty Boy reservoir.
Don't let the prospect of didymo scare you off. Many PA streams have it, too (in fact maybe all of them), it just blooms more in tailwaters. (The Yough has it, both branches of the Delaware have it, and Pine Creek has it.) You may never see it. (Cleaning your boots is always a good idea, though, after fishing anywhere.)
The GP was fishing pretty well yesterday in spite of the flooding everywhere else.
There should still be sulfurs for another week or two.