Spawning is preceded by significant upstream migrations if high spring flows or floods allow.

The purpose of the barriers is to block their upstream migration to reduce reproduction.

Young delta smelt then feed and grow in the mixing zone before starting their upstream spawning migration in late fall or early winter.

As late as 1969, low oxygen levels related to pollution were preventing upstream migration of salmon on the Willamette.

In May 2002, the culvert beneath Highway 84 was identified as an impassable barrier to upstream migration.

Changes in haematology during upstream migration in American shad.

These populations resulted from upstream migrations by fish stocked in Wyoming and Montana.

However, many properly functioning drop structures themselves may impede the upstream and downstream migration of fish.

It is also reported that it follows Catlocarpio siamensis during its upstream migration.

Apparently the main upstream migration begins close to the peak of flood, when the current is very strong and the water is turbid.