This guide is undergoing heavy construction, and will be updated regularly. I'm well aware that there's more to see underwater.
One of the primary activities you can undertake during the day in Coral Island, Diving is both helpful and lucrative. Placing you into the waters on the south end of Coral Island, Diving allows you to clear the seas of trash and pollutants while collecting a heap of treasures. It's a lot of work, and will usually eat up your entire day, but there are enough benefits to Diving that you should check it out.
This guide will cover the basics of Diving in Coral Island. The game is still a work-in-progress, so please note that this guide only covers the first Diving area, located on the docks in the south of Starlet Town. There are hints that more Diving areas will be unlocked as the developers release more of the game.
At the moment there is no in-game map of Coral Island's underwater regions, which can make navigation difficult. Unless you have a strong memory of your surroundings you'll probably get lost. I highly recommend using this map from Twitter to get around. Thanks, @TriforceFusion!
Unlocking Diving
In order to receive the quest that unlocks Diving, Into the Ocean, you need to start a new game of Coral Island and then wait eight days. You'll receive a letter from Ling, one of the head researchers on Coral Island, instructing you to meet her by the docks. Do so and she'll give you the Diving Suit you need to go Diving. Consult the article above for more information.
Diving Basics
Once you have a Diving Suit you can use the boat just south of where you first met Ling to go Diving. This will drop you into an undersea area that's filled with piles of garbage. You can move around similarly to movement on land, though you can't dash underwater. You can slash objects out of your way using your Sickle, and it's the only item you'll need to use while Diving. (Though your Bug Net also gets some use, which we'll discuss below.)
When you first appear underwater you'll be beside a boat anchor. Interact with the anchor and it will take you back to the surface. As you explore you can summon the anchor (X key on PCs) to your current location. This will allow you to quickly return to the surface without needing to look for the exit point, and when you go Diving again you'll return to that exact spot. You can also reset the entry point when you go in for your next dive, which will move the anchor back to the starting section of the underwater area.
While using your Sickle underwater you will continue to use up Energy, as on land. You can eat food underwater if you need a quick pick-me-up, and the recommended food to consume is the Scuba Snack. You can craft Scuba Snacks for ten Seaweed upon reaching the first level of the Diving Skill. Seaweed is available in abundance throughout the underwater areas, making Scuba Snacks an ideal choice for quickly boosting your energy back to full.
Note that your robotic companion will begin to alert you once the time reaches 22:00. At 23:00 Diving will end for the day, kicking you back to the surface. Make sure you've set up your anchor at an appropriate location before this happens.
There are a few things you can accomplish while underwater. We'll start by ridding the ocean floor of all that garbage.
While exploring underwater you'll occasionally come across clusters of colored Kelp. These will start off as Bronze Kelp, and you'll need to collect some to complete an early quest. Metallic Kelp is used to upgrade various facets of your farming - you can permanently upgrade the quality of your seeds, for example - making the collection of the stuff quite useful in the long run.
Kelp can be used to create Kelp Essence using an Extractor. You'll build your first Extractor as part of a quest. Once you have enough Kelp Essence you can trade it in at the front desk of Ling's Laboratory, in the east of Starlet Town, to receive bonuses. You can also purchase more Kelp from this same desk, though if you have the option you should always harvest Kelp. It grows in abundance, refreshes each day, and is quite expensive when purchased on land.
Catching Sea Life
In addition to dealing with trash problems and collecting Kelp you can also catch marine life while Diving. There's a small collection of creatures living underwater whom you can donate to the Museum, give out as gifts, or sell. You'll need to use your Bug Net to catch these animals. Catching creatures underwater is more or less the same as on land, though you can't run underwater, so you need to be especially careful when trying to snag your prey.
Feeding Turtles
Occasionally while exploring the sea bed you'll come across a turtle. It will bar your path, displaying a word bubble containing a piece of produce. This is a toll turtle of sorts, and in order to pass you need to provide it with the fruit or vegetable it wants, at the level of quality it requests. Until you offer up this morsel of food you can't go any further. Fertilizer is recommended if you want to be assured of above-average produce.
Run out of time to feed the turtle in a given season? Don't worry. The turtle's demands will change from one season to the next, allowing you to try again once the seasons roll over. Note, too, that you can give the turtle an item that's better than one they want and still get past. If the turtle wanted a bronze-level Sweet Potato, for example, you could give it a silver- or gold-level Sweet Potato instead.
