It's just a bit of clay that's painted blue and white, thats all!
I was also curious about it because what I can see, floods can occur easily unless they have some kind of precaution taken.
This is a question that needs an answer, so the next time its forecast to rain hard, you need to go back with a little stool and sit by the canal in the rain to watch!
How's your weekend been, Priya? Did you do anything nice?
Take care always :-)