However, here are some options you could use depending on the context:
General:
* Group of divers
* Team of divers
* Party of divers
* Squad of divers
More specific:
* School of divers (for scuba divers, referencing a school of fish)
* Pod of divers (for marine mammal divers, referencing a pod of dolphins or whales)
* Cohort of divers (for a group of divers working together on a specific project)
Ultimately, the best collective noun will depend on the specific situation and the type of diving being done.