Back in the late 80s and early 90s (before the term 'zig rigs' came in) we used to fish an estate lake which had over a foot of soft silt topped with weed growth covering the bottom. A lead would immediately sink deep into this silt and often drag a bait with it.
One of the things we tried where soft bouyant jelly baits suspended from the bottom at half depth and allthough we were after Carp we caught Roach, Rudd, Carp and some large Bream which we didn't expect at mid depth.