Can you identify this please?

I took Mrs booty for an airing this morning, loads and loads of photos taken of many things then I spotted this weird growth in the stream.

It's growing from an area around a rock that is half submerged. The main part of the red plant is part of the grass/weed that is growing from the top left. The red shoots are slowly creeping into the river and outwards into the grassy area. I have seen something similar previously but it was an invasive plant growing amongst gorse and heather on a hillside.

Any ideas from all you botanical types please?