The paved road from Rivas to San Jorge ends at the ferry terminal, where there’s guarded parking (US$3) for your car and a regular boat service to Isla de Ometepe. Up to 18 boats make the trip from San Jorge to Isla de Ometepe (US$1.50 to US$3, one hour) each day between 7am and 5:45pm, though not all sail reliably. Most are ferries headed to Moyogalpa, though some are smaller boats that go to San José del Sur – these are best avoided on windy days if you're prone to seasickness. There's no need to reserve ahead. Passengers simply board and pay on the boat. However, if you're trying to put your car onto a ferry you might have to kill some time: there's often a short waiting list.
Buses leave for Rivas (US$0.25) almost hourly from the ferry terminal.
Alternatively, colectivo taxis between the Rivas bus terminal and the San Jorge ferry terminal should cost around US$1, though some will try to charge at least US$5.
Several shuttle operators in Granada (US$20) and San Juan del Sur (US$18) offer direct, convenient drop-offs at the ferry terminal. If you want to be picked up at the San Jorge ferry terminal and taken to either destination, that can be arranged through lodgings in both towns or on Ometepe; most accommodations can recommend a trusted driver who'll be waiting for you on the dock.