LUTZ — A popular Hillsborough County park was closed indefinitely Wednesday after engineers discovered a sinkhole 90 feet deep and 6 feet wide.The land for Lake Park, at 17302 N Dale Mabry Highway, is owned by the city of St. Petersburg, which leased it to Hillsborough County. The region's water utility, Tampa Bay Water, has five active well fields in the park, which are used to pump groundwater to satisfy the bay area's water needs.All that has made fixing the sinkhole and reopening Lake Park a complicated proposition. The question now is: Who's going to fix it?Hillsborough County Administrator Mike Merrill discussed the "significantly deep chasm" at Wednesday morning's commission meeting. He said the park had to be closed entirely until the county deems it safe to reopen. "The park, the land, is actually owned by St. Pete," he said. "I believe, as the landowner, they would be the ones to pay for the remediation, which will be significant.""We're still gathering information and we have folks going out there to check it out more," said Ben Kirby, St. Petersburg Mayor Rick Kriseman's spokesman.Warren Hogg, the water use permitting manager for Tampa Bay Water, said the utility acquired the well fields from St. Petersburg in 1998. The wells pump water from 700 feet below ground, he said, and had been off since mid July during the usual summer hiatus.Tampa Bay Water resumed pumping Tuesday, Hogg said, but the utility does not believe that contributed to the formation of the sinkhole."If it's not something we could have caused," Hogg said, "we would not pay for fixing it."The sinkhole was first detected Tuesday night by a geotechnical engineering firm, according to Hillsborough County spokeswoman Michelle VanDyke. Sections of the park have been closed for weeks because of summer flooding."We've been dealing with (flooding) for a few weeks now, which is why we hired the firm," she said.Several organizations help maintain facilities at the park, including the Gasparilla Bowmen Archery Club, Hurricane R/C Club and Tampa BMX Raceway Inc. "This morning's call was kind of a shock," said BMX track operator Steven Smith.Times staff writers Steve Contorno and Sara DiNatale contributed to this report.