A number of Ayutthaya guesthouses and hotels can arrange a river cruise. The one organized by the Baan Lotus guesthouse costs 200 baht and accomodates about six people, beginning with a samlor ride to the pier. A small motor boat then takes you clockwise around the island, stopping at the popular Wat Phanan Choeng, Wat Phutthaisawan and Wat Chaiwattharanam for 20 minutes each before passing Chedi Phra Si Suriyothai and returning to Hua Ro market.
The tour is designed to arrive at the picturesque Wat Chaiwatthanaram just before sunset, so if you spend longer than the allotted time at the other temples you'll miss a great photo opportunity.