On a whim, I checked the landing page and saw you'd researched the title before starting. Kudos on that. It's nice when someone takes a little extra time to understand what they're working with rather than just rushing out the first thing that came into their head. It also ensures the title makes solid sense with your adventure design.
Font might be a touch small at printer size for a low quality printer, but honestly that seems to be the standard for this jam. Most of it is black on white, which does help a little. Anyway, cover is visually nice. Vintage, but nice colors and there's a bit of whimsy to it.
Cover is doing a lot of lifting compared to a number of other entries. It's still a full image cover with title, creator, jam, system and level expectations. It then uses the open space to give us an overview and the plot hook table. It's a little cramped, but not painfully so. The plot hooks don't call out well visually, but the trade off is that they don't feel out of place on the cover. It mentions rumors, which made me initially consider it must be a rumor table, but reading it, it's more of a plot hook table. No rumors there, just setup for why to explore. It's a little odd also seeing the mention of an NPC secret in the hooks table, but a quick scan tells me you didn't have stats or extra information for this guy elsewhere. Space constraints.
The map is interesting. The faint hex grid had me pondering for a few moments, but I decided I like it well enough. Even though you can't see it everywhere, the places you can see it are more than enough to know the scale you will be working with elsewhere. The only thing that had me confused was seeing a standard grid inside of the cave spots. It felt out of place like one map was being overlaid on another and removal of the little bits got forgotten.
Sirens aren't special, but depth is added with the sea hag gathering items left in the wake of their actions. That it's not a pure combat situation is nice as well. Negotiation is an option. As to her owlbear, I guess. A lone owlbear on an island is an anomaly, but not impossible. Having it laying an egg that holds value seems odd though since it wouldn't be fertile. Is there a viable owlbear population on this island? How? Are they suffering dwarfism? This is where my mind goes with things like this. I overthink, I admit it. Sometimes a monster is there because you need a monster. Still, of all things an owlbear. It feels really strange to me.
4 had my mind immediately quote “Why does GOD need a starship?” What in the world are they repairing a ship for? Crudely or not, they are a semi-aquatic species. Ships wouldn't really hold value right? Maybe it comes up later. I'll have to watch for that. Maybe this is some clue to a larger story hidden in the text.
Octopus god is a nice callback to the cover. Mimic is pretty average. Not super concerned with it as a trap. Nice it's not just random, but being maintained and fed by the Deep Ones. Onward to them repairing weapons and sailing gear. Weapons make sense, but again, why does an aquatic species need sailing gear? With it now being twice, it feels less like a mistake and more like you're working towards something.
Aboleth 'god' to the Deep Ones is in keeping with theme, but that octopus god feels like it's in contrast now. It might be worth it to add a 'mutation' so the aboleth has grasping facial tentacles to tie it back into that theme. I do love the inclusion of the fish sauce. Incredibly unique and appropriate. Rotting fish in the one version humans find pleasant, plus a potion style bonus.
2d6 Stingbats is starting to feel like a running gag in various modules. A call out perhaps. I'm not someone who feels strongly about Stingbats, but I know some people are incredibly enthusiastic about them. And then back to yet another boat being repaired. At this point I am skipping down to see if there's some sort of payoff for all the sailing supply repairs. And... no. Not really. Looks like it's there just to make sure the players have ship options to escape with. Honestly, you could just have them picking over landing boats left abandoned on the shore from previous folks getting to the island like yourselves.
Ghost. Sure, it works. Dryad? Okay, maybe. How in the world has she held out on this island given how many hostiles are around and she can't exactly leave her location. Fun mechanic with the Treant element though. And then treasures. Nothing much to say. Some decently thematic items in there. Good enough.
Encounter table is smart. Variable depending on location. Having it go off an extra time when changing biomes works well enough. Since the layout was page format, I am slowly learning of the fey folk all over the place instead of reading that back cover to know right away. No shade there, just meant my exploration of this created moments of confusion seeing things like Dryads and Leprechauns seemingly randomly. If I hadn't gone scrolling down looking for the ship issue, I wouldn't have realized the explanation of the inhabitants of the island was noted on the 'back cover' area. Reactions of the Deep Ones don't seem like something that would ever be neutral in this adventure's lore. Perhaps replace it with something akin to 'Flees for backup'. The little explanation why some might react oddly though is nice. Given the dynamics of the island, it explains why some might be hostile or not according to perceived heritage.
On the back, we get the rumor table. It has some nice callbacks to other parts of the document. 'Reaching the Island' section is nice. Good vibes, clarity for why it's dark, etc. Same with 'On the Island'. Wish I'd seen these before reading the interior pages honestly. It would have definitely altered the reactions I was having as I read through. It's not really a fault of your own. Just the nature of reading page style as opposed to spread. It's one of the reasons I offer both to people and will personally read spread versions when they are there. It feels more like picking up a book and reading over the covers before opening the document. At least on a small document like these ones are.
I've never been a fan of random numbers for time to accomplish something. 1 day to get it done and leave is a pretty tight situation. 4 days is almost casual. Having no set number known to the players means you lose that element of control on pacing. And if you hide it from the players, the number is actually somewhat meaningless. They will move assuming minimal time. If they couldn't manage before the timer runs out, they were never going to anyway. If they reach their expected time and end up with more, they'll be wondering if you fudged a number for them. Better to just say a number of days and base the adventure around what a reasonable progress for that time would be.
Ends with credits. Worth having here. Could also have gone on the landing page, but when you can fit it in an actual document, do so. So yeah. Good. Honestly, I think there's a lot to work with in this. There's a set of three main factions (humans, deep ones, fae) with sub-groups involved as well (such as the no-love-lost situation between the Merfolk and the Hag). I happen to know ShadowDark, but this isn't set up in a way you have to. I could easily plug this into a number of games with almost no real effort. Standard trade dress style for a SD game means it immediately reads as one, but isn't forcing you to use that system. Good job on this.