We're really happy you enjoyed the vibe of the game! Yeah, unfortunately we ran out of time for some of the additional elements we wanted to add to the game, one of which was going to be a mini-map to help locate drowning swimmers. Something we'll want to focus on as well as a fleshed out tutorial if we return to the game.
For the throwing mechanic, if you hold down E while not next to a drowning swimmer, it'll show the arch of the throw and will increase and then decrease the range of the throw, releasing E will throw the ring to the spot the arch ended at. It's a bit tricky with the forced movement of the river and some more balancing is needed so it's as usual to use as just going up to the swimmers.
There is no end game at the moment, so it will get repetitive after an amount of play, we'd love to eventually add building mechanics and river expansions, as well as a story mode to delve into the three alien races and the very silly politics between them.
-- Chris