Jet Skis can be launched from most ocean beaches, although you must ride beyond surf lines, and some beaches have special regulations governing their use. The only freshwater lake that allows Jet Skis is El Capitan Reservoir,30 mi northeast of the city near Lake Jennings. Take I-8 north to Lake Jennings Park Road, head east on El Monte Road, and follow signs; there's a day-use fee of $5 per person. Waveless Mission Bay and the small Snug Harbor Marina (4215 Harrison St., Carlsbad, 92008. 760/434-3089), east of the intersection of Tamarack Avenue and I-5 in Carlsbad, are favorite spots. San Diego Jet Ski Rentals (1636 Grand Ave., Pacific Beach, 92109. 858/272-6161) rents Jet Skis. They are open daily in summer; other times of year, call ahead for a reservation. Seaforth Boat Rentals (1715 Strand Way, Coronado, 92118. 619/437-1514 or 888/834-2628.) rents Yamaha Waverunners for two or three people.