Hopatcong State Park sits at the southern tip of Lake Hopatcong, where the lake drains into the Musconetcong River. The beach is a long crescent of pale sand backed by a wide sloping lawn, and it is the biggest piece of this shoreline that anyone can simply walk onto. Nearly all of the lake's nine miles of shore belongs to private homes, marinas and community clubs, so this stretch of state sand carries most of the public swimming on New Jersey's largest freshwater lake.

The bottom is sand and shelves out slowly, which is why the shallows fill with small kids on a hot Saturday. Lifeguards cover two buoyed areas and boats stay outside them. Swimming is allowed only inside those markers and only while guards are in the stands: Wednesday through Sunday, 10 a.m. to 5:30 p.m., Memorial Day weekend through Labor Day. Monday and Tuesday the water is closed even though the gate is open. NJDEP posts current lifeguard coverage on its swimming schedule page, so check it the morning you go.

Lake Hopatcong is watched closely for cyanobacteria. NJDEP samples through the warm months and runs a continuous monitoring station southeast of the state park beach, and it publishes results and any health advisory on its algal bloom map with a color-coded alert index. Conditions change week to week, so read the current advisory rather than an old headline. If it looks like green paint, stay out.

The lake you are swimming in is an industrial artifact. Two glacial ponds were dammed for the Brookland Forge in the mid 1700s at this exact outlet, and in 1831 the Morris Canal Company bought the forge site and raised the water another twelve feet. Lake Hopatcong became the summit water supply for a canal that hauled coal and iron across the state. The park still holds the evidence: the lock tender's house of about 1825, now the Lake Hopatcong Historical Museum, a Scotch turbine hauled here in 1926 from Inclined Plane 3 East, and the stone fountain Cornelius C. Vermeule Jr. designed in 1925. It ran again in July 2024, ninety-nine years to the day after it first opened.

The entrance is at 260 Lakeside Blvd in Landing. The gate runs 8 a.m. to 8 p.m. daily and the office 8 a.m. to 4 p.m. Entry is free from Labor Day until Memorial Day weekend. In season it is $6 for New Jersey plates and $10 out of state on weekdays, $10 and $20 on weekends and holidays, doubled for oversized vehicles. Walk-in and bicycle entry is $3, but walk-ins and drop-offs, Uber and Lyft included, are barred on summer weekends and holidays, so your group needs a car in the lot.

Parking is first come, first served, and on a holiday weekend the lot fills and the gate shuts until cars leave. Arrive early and arrive together. The bathhouse behind the sand has restrooms, showers, changing rooms, a first aid room and a concession. Grills, tables, a picnic shelter and two playgrounds sit on the hill above the lot, with sand volleyball courts and a boat ramp at the north end. Rafts, inner tubes and pool floats are not allowed in the swim area; only Coast Guard approved life jackets are. Dogs are barred from the sand and the water, alcohol is banned parkwide, and the park keeps no trash cans, so whatever you carry in goes home with you. Fishing is good here but not on the beach or inside the swim area, and hiking means short walking near the office rather than a trail system.