Case Law regarding Riparian Rights and Responsibilities

Under UK common law, landowners have 'Riparian' rights and responsibilities regarding watercourses that flow through their land.

Using UK case law history, I need to know who is responsible for these rights/responsibility if the land is occupied under a lease. Still Landowner or leaseholder tenant?

Quickish turnaround required.

(Not sure on cost's hence just picked £100 as reasonaible figure)

Thanks,
Hummad