I feel I'm stagnating in this job.

我觉得，干这份工作我没有长进。

Industrial production is stagnating.

工业生产停滞不前。

The water in the pond was stagnating.

池塘里的水逐渐变成了死水。

If you're not changing, you're stagnating.

如果你不去改变，那么你就是停滞的。

If you're stagnating, you're falling behind.

如果你是停滞的，那么你就会落后。