Upstream means moving or located in the direction opposite to the flow of a river or stream, toward the source where the water begins. When salmon swim upstream, they fight against the current, pushing their way back to the place where they were born to lay their own eggs. It's hard work: the water pushes against them the whole way.

The opposite is downstream, which means going with the flow, letting the current carry you along. If you drop a stick in a creek, it floats downstream naturally. But hiking upstream requires effort because you're working against the water's natural direction.

People also use upstream to talk about earlier stages of a process. In business, upstream activities are the earlier steps in making a product. For an oil company, upstream work means finding and drilling for oil, while downstream work means refining it into gasoline. In manufacturing, upstream problems are issues that happen early in production, before the final product is made.

When someone works upstream on a problem, they're tackling the root cause rather than just dealing with the consequences. If your school has a litter problem, cleaning up trash is downstream work, but teaching students not to litter in the first place is upstream work.