It's life Jim, but not as we know it.....

Let's have a multiple choice quiz. What can you see in this photo?

Is it a) an attractive bridge over a grassy pathway... or b) a bridge over a canal that has been completely overtaken by some algae-like life form? (The answer is, in case you didn't guess, the latter).

I took this photo as I cycled to Grace's playgroup last week - it's on my route there (and a beautifully scenic route it is too!). This is a canal in Wassenaar, similar to many around The Hague and, over the last few months, I have witnessed so many waterways become completely green on the surface to the extent that the water is completely hidden. I have Googled this and cannot find an explanation - biologists, can you explain?

Should we be worried about what is happening with our water? Will this life form disappear as the cold winter months creep in? Is this normal? I don't know the answers to any of these questions but I'm sure someone does. Until I have the answer, I shall continue to look at ponds and canals that appear to be patches of grass. Let's just hope that nobody tries to walk across them by mistake!