Install fence for deep brook running through yard?

[Doreen Morawski]

I am turning my private home into my first rental property this summer. I have a brook running through the yard with a high bridge going over it. The bridge goes from the main yard to another section of fenced in yard. There is no railing on the bridge. The water is not deep but it's a 5 foot drop down to it. For liability reasons, should I install a fence along the water and put a gate in front of the bridge? What if an unsupervised child tenant falls in? Is this something I should even worry about? See photo.