Lovely game! Everything feels very polished, in particular I like the clear enemy triggers and how smooth the ducklings' pathing feels. The hazard progression is very well thought-out, although the plastic bags may be more of a help than a hinderance. I spent quite a while playing, both to try and beat the levels and then to shoot for the gold targets!
Unfortunately, the balancing in the later levels isn't well tuned. With both snakes and beavers in the mix, so many of the ducklings die before you have any chance to collect them. Combined with the punishing enemies and ever-increasing targets, the last levels are a slog. I persevered to beat level 5, but the successful attempt alone clocked in at almost 10 minutes! One way this could be improved is if the ducklings were invincible when they spawn, perhaps indefinitely until you pick them up. Another idea is that the duckling spawn rate could increase as you progress through a level: this would also make losing all of your ducklings less tragic!
Overall, it's a great game, and I had a lot of fun with it! I think it would only take a few tweaks to sort out the last levels and make it even better :)
P.S. I played level 6 for 5+ minutes, and although I didn't clear it, I didn't see any turtles either. Did you run out of time to add them to the game? I'm curious what their behaviour would have been!