If you are worried about soft silt, get a long prodding stick and poke around in the margins. Alternatively, tie on a few foot of light coloured wool on your line and attach a heavy lead and let it sink in and see how much of the wool is discoloured. If it is quite deep, as greeksil says try a PVA bag with a lightish flat lead or a pva mesh stocking of bait on a longish supple braid on a helicopter rig rather than a lead clip.
This time of year, it's all about the windows of opportunity that arise when the temperature climbs or a low pressure system comes in. Plot where the sun is shining when it is at it's maximum and aim for that area. This time of year, shows can be pretty rare and if you don't have any previous knowledge to go on, it could be a struggle.