There is a discussion of the water issue at TripAdvisor's Sanibel Island forum.
By December, the water releases may have ended. Sea Six may know more about that. Certainly the folks posting at TA's forum will keep us informed.
In addition, the water (when we go) always tends to be murky, at least along the shoreline because of the tide action. There is also tannin in the water. So, Sanibel water just isn't the clear, blue water you find in the Caribbean even without the water releases.
HTH