Fishes are caught when they are on the way upstream to lay eggs.

鱼群在前往上游产卵的途中被捕获。

youdao

Salmon manage to swim upstream to lay their eggs.

三文鱼设法游到上游产卵。

《柯林斯英汉双解大词典》

Grizzly bears gather at prime fishing spots during the summer, when salmon run upstream to spawn.

夏天，鲑鱼会洄游到上游去产卵，于是灰熊就在这条路线上找一个最好的位置呆着捕鱼吃。

youdao

"Every fish we take out there is one less fish to challenge the electric barrier further upstream yet."

VOA: standard.2010.07.19

It provided a calm, safe route west next to the river, which is nearly dry upstream part of the year but whose rapids rage in springtime.

VOA: standard.2010.04.29

To fully experience the Douro Valley, however, head upstream to the Alto Douro (Upper Douro) wine region.

BBC: The changing landscape of the Douro River Valley

My evolution continued as I moved back upstream to the East Branch, probably the least familiar of the three branches.

FORBES: Catskills Fly Fishing Book

Every year, the Rogue is filled with salmon swimming upstream to spawn.

WHITEHOUSE: President Obama Speaks at Conference on Conservation