Movie with mermaid and mysterious lake

[wositelec]

It is a water that turns teens into fishes.

I can't remember the name of this movie and it's driving me crazy. It was made around 10 years ago and was a British horror about these teens who hang out at a hazardous lake/river and get infected with something that causes them to mutate. The main character is a boy with a strong Scottish accent. At one point his sister gets a rash/wound on her back after being exposed to the water, and when her friend tries to clean it for her the wound opens up because what's happening is that she's growing gills like a fish. At the end you see her floating in a tank, and she's changed into some type of mermaid/fish thing. It wasn't a very good movie but it's really annoying me that I can't remember the name or find any trace of it. Does this sound familiar to anyone?

[wositelec]

SOLVED

"Weaverfish" (2013)
"After spending the night partying at a condemned river creek, the atmosphere is soon lost for quiet teenager Reece and his friends. Headaches and heartaches give way to a terrifying race back to civilisation as a grossly disfiguring virus takes hold on the most vulnerable."