Blue Marsh Lake's swim beach sits in the Dry Brooks Day Use Area on the north shore, a few miles northwest of Reading. The lake is a U.S. Army Corps of Engineers flood control reservoir on Tulpehocken Creek, roughly 1,147 acres of water inside about 5,000 acres of Corps land, and Dry Brooks is the designated swimming area, the one stretch the Corps marks with buoys and tests through the season.

The setup is more park lawn than seashore. A wide mown slope runs down from the picnic tables and pavilions to the waterline, and the last few feet before the water are sand mixed with flat, water-rounded pebble. Entry is gradual. You can wade a long way out before the bottom drops, which is why the place works for small kids, and a line of buoys and steel posts marks how far you are allowed to go. Toward the east end a few large boulders sit half submerged in the shallows, obvious on a calm day and easy to bark a shin on when wind chops the surface. The water is green rather than clear, typical of a warm Pennsylvania impoundment, and visibility drops off past knee depth.

There are no lifeguards. The Corps posts that plainly at the waterfront: swimming and wading are at your own risk. There is also no entrance fee and no parking fee. The Corps charged three dollars a vehicle at Dry Brooks until January 2016, then dropped the program because collection cost more than it brought in, so the beach, the lots and the restrooms are free. The only money that changes hands here is for the three group pavilions, Lakeview, Hillside and Vista, reserved through Recreation.gov.

Hours move around. The baseline is 8 a.m. to dusk, but staffing cuts in recent seasons have closed things earlier, with the 2025 season posted at 8 a.m. to 6 p.m. and all swimming ending at 5 p.m. Read the sign at the entrance rather than trusting an older listing.

The rules are stricter than most lake beaches. No inflatables of any kind in the swim area: no tubes, rafts, noodles, boogie boards or arm floaties. Coast Guard approved life jackets are the only flotation permitted. Alcohol is banned everywhere on Corps property, dogs are not allowed on the swim beach or the picnic areas beside it, and there is no camping anywhere at Blue Marsh, on land or on the water. Charcoal grills are scattered through the picnic area first come first served, but bring your own charcoal, and personal grills are not allowed in the beach and towel area.

Water quality is the thing to check before you drive out. The Corps samples the swim area through the season, and the beach has been shut more than once for high E. coli after heavy rain. Blue Marsh has also drawn cyanobacteria advisories in recent summers. Current status comes from the park office at 610-376-6337, and Pennsylvania DEP keeps a harmful algal bloom page worth reading first.

Weekends fill. Beach parking is in the lots above the concession stand, and on hot Saturdays the boat ramps stop admitting trailers once they hit capacity and reopen in the evening. Come early. The Fox Trot trail leaves from the day use area if you want to walk off lunch, and paddlers put in along this shoreline, though motorized boats have to use the Dry Brooks ramp half a mile east instead.