The tide, a natural rising or falling of water level, appears as an event at the start of each Salmon Run shift. This can limit or expand the area a team can work with in fending off the Salmonids.
High tide[]
The water level rises sharply and your work area is smaller, meaning that the bosses spawn near you. Sounds easier than normal but it isn't, and the chances of a crew wipe are high.
Low tide[]
The water level lowers and the shore can be accessed. The rest of the shift will always happen at that said shore, and the egg basket will spawn there. If you see a "This Way" coming from where the Shore is, RUSH over there, as you will have but a small time to even just lay enough ink to move around.
All tide changes come with an audible wave sound. A rising tide sounds like a wave hitting the beach (calm), but a lowering tide sounds more like being near a waterfall, and is clearly audible when sound is on.
Another way more effective way of knowing which tide is incoming is to look at that semi transparent wave that appears when the 10 seconds countdown at the start of a wave is between 10 and 6, as seen on the screenshots on the right >>
They represent successively high tide, normal tide and low tide.