Among more than 700 natural springs in Florida, Silver Springs might be the best known and most loved. Near Ocala, it has drawn visitors — including swimmers, scuba divers, glass-bottomed boat riders and Hollywood film-makers — for decades.But the flow of groundwater that sustains Silver Springs has been plummeting. Some experts blame too much pumping from the underground Floridan Aquifer. Others arent sure.Yet, even with the future of Silver Springs in peril, the district agency entrusted with managing water resources in the region is considering a request to pump up to 13 million gallons a day from the aquifer for a new cattle ranch nearby.Yes, theSt. Johns River Water Management District, which tells homeowners when they can and cant water their own lawns, is considering issuing a single permit that approaches the amount of water the entire city of Ocala is permitted to use.If the districts leaders truly believe in their own mission — to “ensure the sustainable use and protection of water resources” — they wont even think about granting the ranchs request until much more is certain about whats causing the decline of Silver Springs and the regions other waterways.The district says its staff will evaluate the “possible impacts” of withdrawing so much groundwater in deciding on the permit application from Adena Springs Ranch. But the ranch could get its permit by the end of 2012, even though the district isnt expected to agree on what should be the minimum water flow at Silver Springs, a key metric for protecting it, for at least another year.