If every river ends somewhere, how much of ocean pollution actually begins inland?

We often talk about ocean pollution as though it begins at the coast. Yet rivers can carry litter, nutrients and other pollution from places far inland.

So where should ocean protection really begin?

The route from a street to the sea is not the same everywhere. Rain, drainage, waste collection and the shape of a river basin all matter. Some rivers never reach the ocean, and pollution can harm freshwater life even when it stays inland. It would be useful to compare prevention near the source with cleanup farther downstream, rather than assume one answer fits every place.

• Where does water from your neighbourhood go? • Who could prevent pollution before it reaches a river? • Which local change would you start with?