Sunken crates are a rare fishing drop, not a shop item. The fishing guide is explicit: the base fishing area cannot produce them. The second fishing-area expansion costs 20 million cash, and the sunken pool is behind that purchase.
Levels that change what an NPC can catch
Open Manage, then Fisherman.
- Level 4 is the deep-pool breakpoint. NPCs then have a reported 10% chance to fish an active deep pool or whirlpool on their own.
- Level 5 lets them equip better rods.
- Level 8 is the listed gate for a carbon fiber rod.
Rod prices in that guide: a carbon fiber rod at 800 million cash, and a golden rod at 2,000 diamonds. The golden rod is the best listed rod for an AFK NPC setup. It is not required. A carbon fiber rod, or a strong rod on level 5+ fishermen, is described as enough to hunt crates.
How to spend the rare windows
Luck portals are a 2x luck multiplier while they last. Whirlpools and deep pools are called common. When one appears, fish it yourself, then let the leveled NPCs continue. The same guide's expectation with a strong setup is roughly one or two crates per two hours, and some players report long sessions with none. Do not buy the 20M expansion until the restaurant can spare it. Crates are a late target, not a starter income plan.
A separate fishing-layout note mentions a Davy Jones Organ at about +65% cash and quality stations that raise rarity. Those are furniture bonuses on a fishing floor, not crate requirements.