Fog

Fog is a Known Occurrence in Salmon Run.

Description
Fog will cover the battlefield during this event, making it more difficult for players to see. Additionally, Salmonids spawn all over the map instead of concentrating on a single area at a time. Although it is said to be rare, at least two Goldies will spawn during Fog, so keep an eye out for them.

Salmonid Field Guide
The following text is quoted from the Salmonid Field Guide.
 * What Happens
 * The area is covered in a dense fog, drastically reducing visibility.
 * Enemies will take advantage of the fog and attack from all directions.
 * How to Get Golden Eggs
 * Defeat Boss Salmonids.
 * The extremely rare Goldies may appear in foggy conditions.
 * Advice from Mr. Grizz
 * Try to maintain contact with your teammates at all times while in the fog.
 * Being alone in the fog is extremely dangerous.
 * Supplementary Information
 * Goldies are extremely rare Salmonids&mdash;only one of every 10,000 hatchlings is a Goldie.
 * They live longer than and possess far superior intelligence to normal Salmonid specimens.