@PenguinFoop According to SimsVIP.com
The following diving items can be purchased at the deep water buoy:
Diving Knife (§250) – Allows Sims to dive and collect Seashells.
Spearfishing Gun (§500) – Allows Sims to Spearfish
Rebreather (§750) – This item unlocks Scuba Diving for Sims. Unlike Free Diving, there is not a Fitness Skill requirement for Scuba Diving. Once a Rebreather is purchased, Sims can Scuba Dive immediately. Mermaid Sims do not have the option to Scuba Dive since they already have the ability to Free Dive.
Underwater Camera (§1,000) – This is used to collect 10 unique photographs for your home. Sims can only use the Underwater Camera if they own the Rebreather (or are a Mermaid). The Underwater Photo Collection is not considered an official collectible so you can’t track your progress in the Household Collections menu.
Treasure Tool (§1,200) – This is the most expensive item, but allows Sims to search the ocean floor for valuable buried treasures. This is the fastest way to complete the new Buried Treasure Collection and can be used with or without the Rebreather. Once Sims own the Treasure Tool, they can choose to Free Dive or Scuba Dive for treasure.