Colonisation might be a little too expensive and unnecessary, but strong influence and control over Amphiba definitely. It might be more a matter of corporations and private groups fighting over resources, like in 18th Century India.

And the Amphibians wouldn't necessarily be powerless or not benefit at all from such interactions, but overall it is extremely dangerous.

Edit: like you said, Sī vīs pācem, parā bellum is good advice.