So nobody is responsible for the results of their actions?

If I sand my boat at the same time you're varnishing yours in an adjacent slip,
and the wind carries my dust into your work, am I exempt from any responsiblity
because the dust landed beyond the confines of my own slip? Should I respond to
your righteous protest with "Tough, dude. Deal with it. You shouldn't expect to
be able to varnish- everybody knows that sanding is a common activity in a
marina."

Upstream activites that accelerate silting
can be reasonably found responsible for proportionate shares of the accelerated
silting. Upstream taxpayers should participate in clean up/ dredging costs.