Does anyone know of an outstanding whitewater adventure near Lima?

Lima is not in the mountains, hence no white-water rafting. You could probably walk up the Rimac before you could float a raft in it.

Be careful of whitewater rafting around Cusco/Urubamba. If you flip and swallow water you will need a course of antibiotics. Probably true of pretty much every river there.

Try Apurimac River, it's an unforgettable 1-day experience.

Other than being in the same country, that isn't near Lima. I guess it depends on how one defines near.

Make liberal use of the map function when you Google. Or use Viator/ Tripadvisor if you aren't already in Cusco.

There used to be a good online travel guide called Andean Travel Web for some basic research. Unfortunately much of the web and printed material won't be updated.

....