Flawed.
Tammy only moves in bursts, which gets annoying when more things get onto the screen at once, all falling much than actual garbage would sink in the ocean (though much of it doesn't sink at all... I'd wager that no amount of charity money would be necessary to save Tammy's ilk from the apocalypse of broken fishing hooks that this game puts into the virtual waters).
The game has no real point to it. Technically it's an avoidance game, but as high scores are not tracked or submitted anywhere and there's no endpoint, whether I immediately let Fred eat Tammy or whether I go for 10000 points the game treats the accomplishment exactly the same. And believe me, the game itself isn't interesting enough to have no ending.
If you wanted to make an advocacy game, putting real statistics in, giving an enjoyable game that makes your point rather than an un-enjoyable game asking me to donate, these are the things that you'd want to work on.