The best thing about using watercourses as your heat source for heat-pumps - the water flow naturally takes away your "colder" output and brings you more "warmer".

Ground source heat pumps are limited because the ground they have chilled stays stubbornly in the same place, so the only way you can extract more heat from it is to make it even colder, which gets less efficient. Watercourses don;t have that problem.

The opposite effect is also why thermal stations (including but not only nuclear) are usually on the coast or near large rivers: you can dump a lot of water heat into water and have it carried away.

Not always good for the local ecosystem without mitigation, but at least one Japanese reactor allowed local colonisation by tropical fish and local legend said the same about Sizewell.

Sizewell C claims to plan recover waste heat and use it for carbon capture somehow, about which all I can say is a big old hmmmmm.