1. To return, we had to go across a stream, but the water rose very quickly.

2. To return, we had to go across a stream, but the water became high very quickly.

(Are both the same?)

3. To return, we had to go across a stream. Suddenly the water reduced very quickly.
(Can we use 'reduced' as the opposite of 'rose'?)

1 answer

Yes, both one and two are the same.

Yes, you can used reduced as the opposite of rose.