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It looks so cool there. Thanks!

The lighter bottom of the river you mean? If you go to this post: https://ecency.com/hive-194913/@littlebee4/walk-around-16th-century-burghley
Scroll down a bit.

You see a better angle of the river next to the bridge. I also have another link there to what it is. It is basically a track for horses to cross during the world famous Burghley trails / races. It is one of the largest events there.