Cause CMake to find different VTK?

I have the standard VTK libraries installed (mostly for use in Python), but I would like to try to build a C++ project, and use a different set of libraries in ~/opt/vtk. How would I give CMake a hint to look there first, instead of in /usr/lib/x86_64-linux-gnu/cmake/vtk-9.1?

-DCMAKE_PREFIX_PATH=~/opt/ or -DVTK_DIR=~/opt/vtk/lib/cmake/vtk.

Thanks @mwestphal, that worked like a charm.