Fontainebleau State Park sits on the north shore of Lake Pontchartrain about three miles southeast of downtown Mandeville, and its sandy lakefront strip is one of only a handful of Louisiana beaches the state formally designates and tests for swimming. The Louisiana Office of State Parks runs the 2,800 acre property from 62883 Highway 1089, Mandeville, LA 70448, reachable at 985-624-4443. The park opened in 1942 on what had been Bernard de Marigny's sugar plantation, and the brick chimney and walls of his 1829 mill still stand near the entrance road.

Swimming is allowed and the beach stays open, but the water quality record deserves a hard look before you plan a trip. The Louisiana Department of Health has sampled this shoreline weekly since 2004 as station FNTB1, EPA identifier LA733869, covering 0.15 mile of beach. During the 2025 season the site posted an enterococci geometric mean of 36.5 MPN per 100 milliliters, above the state threshold of 35. The beach spent 111 days under a swimming advisory, about 61 percent of the available season, and was open and in compliance only 39 percent of the time. It was never closed. Louisiana issues advisories rather than closures, so the gate stays open and the call is yours. Sampling runs May 1 through October 31 and results post every Thursday. An advisory triggers when a weekly sample tops 104 MPN per 100 milliliters or the 30 day running geometric mean tops 35. Counts climb after heavy rain on the north shore, so the days right after a storm are the worst bet.

The water itself is only faintly brackish. Health monitors logged an average salinity of 1.5 parts per thousand here in 2025, against roughly 20 at the state's Gulf beaches. The bottom is soft and silty and the grade is gentle, staying near two feet deep well out from shore, which suits small children but means wading rather than diving. No lifeguards are posted. A south wind builds a short chop across open water with nothing to block it.

Entry costs $3 per person, with children 3 and under and seniors admitted free. Gates open at 7 a.m. and close at 9 p.m. The entrance station is staffed 8 a.m. to 5 p.m. Sunday through Thursday and until 8 p.m. Friday, Saturday and the day before a holiday. A bath house stands just off the sand, and the water playground beside it runs 8 a.m. to 8 p.m. Tuesday through Sunday, closed Mondays for cleaning. A concrete fishing pier with a covered gazebo at its end reaches into the lake next to the swim area.

Camping is extensive. There are 96 premium pull-through sites at $33 to $49.50, 37 unimproved sites at $18 to $27, primitive group camping from $35, twelve cabins at $175 to $262.50 and a lodge at $250 to $375, plus a $4.50 reservation fee. A 4.8 mile hiking trail and a 1.2 mile nature trail with a marsh boardwalk leave from the day use area, and the paved 31 mile Tammany Trace rail trail cuts through the park. Kayak rentals run $35 to $80, and paddlers put in on Cane Bayou and Bayou Castine. Birders have recorded more than 400 species on the property.