system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do underwater prey know a predator is hunting them?
gpt
Through all the usual senses you'd find in creature on land. They might see the predator, hear it (water is a much better conductor of sound than air), "smell" it in the water, or feel something disturb the currents around them.

Some sea creatures even have what we would consider extra senses. They may be able to pick up on electrical activity, echolocate, or see into spectrums that we humans cannot.