The bag itself would probably deteriorate reasonably quickly but they all have a plastic liner to deter moisture that would last a while and you probably wouldn't want it to contaminate your BOW.
I just dumped a load of 3" rock at the edge of the water and spread it down into the water for a ways and works pretty good for a boat ramp.
Have done it on a couple ponds already. works best if you do it before the pond is full but can be done afterwards with a mini excavator to add it on further out into the water.

All the really good ideas I've ever had came to me while I was milking a cow.