Tigers are incredibly stealthy and very good swimmers. During a river cruise in the Sundarbans, I had a local boatman on the river launch who had been attacked by a tiger. The boat which was carrying some live-stock (goats and chickens) to the weekly bazaar had anchored for the night (boats can't navigate in the confusing riverine delta in the dark) and the boat-man (majhi) was dozing on the deck. The tiger (probably attracted by the scent of the live-stock, had swum out to the boat and leapt on deck. The man had barely time to react and a fling a lighted "hurricane" lantern towards the tiger. The tiger took off into the water again, but not before taking one of the man's ears and a good chunk of skin and flesh off his back. That is how I saw the boatman a good 6 years after the event.
Another point of note, the tiger usually hunts alone; while the lions hunt in groups. The tiger is far more ferocious than a lion; foresters claim that the lion's ability is largely hyped.