As Theo mentioned aeration should help a bit with the organic stuff. You can accelerate sludge removal by a process called bio-augmentation or bio-manipulation in which you add beneficial microorganisms to the pond. Coupled with aeration, these critters will consume organics, reduce nutrients and therefore will even help reduce algae and improve water clarity. In my opinion, this should be a periodic activity in almost all long term, sustainable lake/ pond management plans.
