FWIW the stink will begin to go away once the muck on the bottom switches from anaerobic to aerobic decomposition, and the muck will decompose much faster as well. However, the decomposition process will add more nutrients to the water column making for a more fertile pond. Sure, the ecosystem will love it, but the plants will too which is counter-productive for swimming in some circles unless you like flossing with pond plants.

If you have the ability to direct downspouts and non-fertilized surface water into the pond to assist in flushing old nutrient-laden water out, that will help some. Adding dye to the pond (I prefer green and black combo, some like it blue) will reduce plant growth on the bottom making for better swimming conditions.

Which reminds me: Do not use chemical fertilizers on your lawn. That will get into the pond and turn it into an un-swimmable hole. Only organic low phosphorous fertilizers.