FranciscoB
Fishaholic
This is well intended but not useful, and not true. There is no such thing as generic “river rock” - if one is in Ohio, Kentucky, Indiana (these are just examples), the overwhelming majority of hard substrate in streams is limestone. That is a sedimentary carbonate rock that WIlL affect pH.
Igneous rocks, found in some streams and elsewhere swill not affect pH.
The rocks shown in the last photos (igneous) will be stable. Most carbonate rocks will not be stable, and some are very common in streams.
