This is not the first gate that has halted your progression in Aurvangar Wetlands in God of War Ragnarok. Yet this one is twice the size. Here's a guide on how to open the big gate in God of War Ragnarok.
Where to find both chains to open the big water gate in Aurvangar Wetlands in God of War Ragnarok
To get past the big water gate in Aurvangar Wetlands in God of War Ragnarok. You need to locate two chains, to lower the gate entirely, allowing your boat to pass. Here's where you can find the two chains.
Where to find the first chain to open the gate in God of War Ragnarok
The first chain to open the gate in God of War Ragnarok is just after you have killed the Ormr. Go right from the wooden platforms to see a massive anvil. Break the lock on the anvil by throwing your axe at it. Climb on it, and you'll see a chain in front of you. This is the first chain to open the gate. Use it.
Where to find the second chain to open the gate in God of War Ragnarok
To find the second chain, head left of the first chain, and you'll come across a water geyser. Throw the Leviathan Axe into the base of the water to freeze it, and jump across. Kill the enemies that appear, and you'll find a locked geyser. Uncover it using your Blades of Chaos, then freeze the geyser on your left.
Freezing the other geyser will increase the geyser's power on the right, which turns the wheel and lowers the massive anvil. However, due to the wooden boards, you cannot break the lock when entirely dropped. Now is where speed comes into play. Recall your axe by pressing triangle, and the anvil will start to rise. You can now see the lock and have the time to throw your axe and destroy it.
Return to the anvil and climb it. But there is nowhere to go. While on the anvil, look towards the water geyser turning the wheel, and throw your axe at its base, freezing it. The geyser underneath the anvil will become stronger and lift it. Step off into a new platform with a Kvasir poem in front of you. A chest to the right and then the second chain to open the gate so you can progress.
For more God of War Ragnarok guides, we've got you covered. Check out How to shut down Althjof's Rig for the Favor In Service of Asgard in God of War Ragnarok and How to ignite all three torches at the locked chest in Jarnsmida Pitmines in God of War Ragnarok at Pro Game Guides.