You need to travel and visit specific locations to have particular creatures spawn in them in Animal Crossing: New Horizons. For example, if you’re looking to catch a citrus long-horned beetle, you can only capture it while it rests on a tree stump. You won’t find it elsewhere. It helps to understand where a fish or bug naturally lives to hang out there. For those curiously looking for a sturgeon, salmon, or king salmon, where is a river mouth?
The river mouth is a straightforward location to find in the game. It’s where the river and the sea meet on one of the islands. You can find this on your island or on one of the other islands you visit elsewhere while out on Mysterious Tours. You will know you’ve located the correct position when you see many rocks underneath the water. The fish thrive in this location greatly enjoy swimming through these rocks.
You can catch several different fish that live here. Make sure you bring several pieces of fish bait to increase your chances of having the harder to locate fish and bring them to you. If you fail to capture them while visiting other islands, yours should have at least two different locations where the river meets the sea. You can fish on the beach area or the grassland, as long as you toss the fish bait into the rocky location, you should be good to go.
Always be on the lookout for the notable areas bugs and fish naturally live because if you’re having trouble finding them, chances are they only show up at a certain point. The more you modify and learn about your island, the more wildlife you can find and bring to Blathers’ museum.