Hilo
This is most likely the place she means: a lagoon walled off by lava rock and reef, fed by cold freshwater springs that float over warmer seawater, so swimmers feel both temperatures at once — 'mélange d'eau douce et d'eau salée' at '10 minutes d'Hilo'. Richardson Ocean Park further along the same road also has brackish water but is better known as a black-sand snorkel beach. Green sea turtles feed along the reef; keep at least 10 ft away. Lifeguard coverage is reported differently by sources (daily vs weekends, holidays and summer, 9:30 a.m.–4:45 p.m.), so do not promise a lifeguard; ask about conditions and stay out when surf is high.
Free entry and parking; county park open 7:00 a.m.–8:00 p.m. About 4 miles (5–10 minutes) east of downtown Hilo on Kalanianaʻole Avenue. Roadside parking is limited — use the larger lot at neighbouring Kealoha Beach Park, a short walk away. Restrooms, showers and picnic tables; no sand, only lawn and lava steps into the water, so bring water shoes.