Translation:A yellow lion drinks water by the river.
There is a good description in another thread by a geographer about the meanings of bäck, å, flod/älv which suggests to me that the most accurate English translations would be creek, stream and river respectively. On that question, I put stream for å and it was accepted, but the suggested translation was river. On this one, I put stream again; it was rejected and the suggested translation was creek! Anyway, I'm going to submit that stream should be accepted here, but I wonder if maybe the course should choose the most precise translation of each and accept only that, to teach the difference?
Yes, it's clearly a bit of a grey area. One man's river is another man's stream in English and it seems to be the same in Swedish.
It's probably the same with other words that imply a continuum of sizes (like pebble, rock, boulder in English).
Thanks for the Wikipedia article; the photograph does suggest to me that å probably can stand for something a bit larger than what I would call a stream in English, so duolingo is probably right to not strictly enforce that translation. (Although, I would regard creek as smaller than stream, so if the former is accepted, I'm sure the latter should also be.)