Yes, though if (SPF30 and above) used correctly (applied in sufficient quantity and frequency) it is extremely unlikely.
No sunscreen actually blocks out all UV light, so it is theoretically possible if one had no natural protection from melanin (like those with albinism) and were outdoors from dawn to dusk in the hottest conditions by water (added reflected UV). What is more likely is that insufficient has been applied, not enough time has been given for it to soak in before going into the water and an extended time has been then spent in the water without reapplication straight after toweling.
