Well done on creating a beautiful underwater world and great use of the theme! I loved the aesthetic of this - the color palette and also attention to detail in the artwork like how it gets darker as you go down and there are small lights around certain underwater fauna. The world feels interesting to explore (I used debug mode to swim around and reach the bottom flag)
However i just couldnt get past the first area using the jump mechanic. As others have pointed out, its a bit too difficult and i tried with many different angles but couldnt get through. Good that you kept the debug option, even just exploring without the jump felt satisfying.Maybe giving some control to the player after he jumps or giving the player an option to set the angle could be mechanics you can think of adding so that the player feels that they have agency over the outcome. Also maybe giving some way for the player to see which differnet species are collected can also add to the exploration fantasy. The music is really good and fits the vibe of the underwater atmosphere.
I think its a really solid concept and just tweaking the gameplay mechanics and difficulty a bit would make this really fun to play!