I agree with Stu get down there at dawn or dusk and just watch, dont concentrate on one are just look out over the water the slightest movement will become apparent, walk the banks looking for signs of fish scales dead fish etc, if there are fish you will soon see em and to be honest I cant imagine any water (unless it has just been dug) not holding fish, they spread so easily.
Agree with fish it camp,just got back into fishing after 10 yrs away and was fishing the day ticket venues(great fun and got my basics back upto scratch but something was missing).Had best days fishing/watching so far on an overgrown non navagable strech of canal were like you im wasnt even sure there`s fish in it sat from 16.00 to dark on a blank but it was great got 2 bites!!.also ask in nearest pub if no joy go to tackle shop nothing there then ask on internet about the place(always found pub to be key)look around the banks for bait/genral fishing litter. ive been given great info and found out to my surprise that it holds great fish but is very hard due to being only 5ft foot wide in parts and only a couple of feet deep and crystal clear,but tench to the 5lb mark,mirrors of 12lb and grass carp about the same.cant wait for things to get a bit warmer.
fishing for me now is all the better when even a bite is a result,turn the bites into fish and then target what you like be it silver fish ,tench/carp or even pike/trout.
happy hunting and tight lines.