A wet dirty--as trapped water is bound to become--bilge is a primordial soup that can make a whole boat smell like a swamp or even a sewer, and it doesn't take any dead animals to do it. There SHOULD be adequate limber holes in stringers, but not all production builders can be counted on to reliably put them in. That makes flushing out trapped water very difficult, if not impossible. Just dumping bleach into the mix is not the solution.
Creating access to the bilges is only good solution. That requires installing a couple of hatches (something else that few production builders ever do, but should) in the cabin sole to provide the access needed to keep the bilges clean. When I restored an old boat, one of the best things I did was put a 12" wide hatch over the centerline that ran almost the entire length of the cabin, breaking it up into 3 sections lengthwise to make it manageable to lift out. Countersunk pull rings left no "toe stubbers" in the teak parquet sole. That gave me access to the entire bilge. You may not need anything that long, or two separate hatches might work better on your boat. Cost isn't pocket change, but it's not outrageous either...and a PERMANENT solution to a problem that not only ruins life aboard, but can even have health implications if you're allergic to molds. It's an improvement that can even value to your boat, if not in actual dollars, in a lot more "saleability" than a boat which stinks has.