You can start fishing anywhere near the water, but there is some spots with better items, I will describe the spots types below and what they provide each.

As of now there is no obtainable items in the game that grants fishing luck modifiers, but I included the probabilities calculation for it just in case.

This guide contains all fishing spots and the catch probabilities in game as of v1.2.1

Currently there is 11 spot types in the game
There is a +-20% random modifier applied to the catch duration
Attempts before depleting: 5
Catch Duration: 15 seconds
Items:

Attempts before depleting: 8
Catch Duration: 11 seconds
Items:

Attempts before depleting: 10
Catch Duration: 10 seconds
Items:

Attempts before depleting: 6
Catch Duration: 9 seconds
Items:

Attempts before depleting: 8
Catch Duration: 10 seconds
Items:

Attempts before depleting: 6
Catch Duration: 10 seconds
Items:

Attempts before depleting: 6
Catch Duration: 12 seconds
Items:

Attempts before depleting: 5
Catch Duration: 16 seconds
Items:

Attempts before depleting: 5
Catch Duration: 15 seconds
Items:

Attempts before depleting: 6
Catch Duration: 15 seconds
Items:

Attempts before depleting: 8
Catch Duration: 12 seconds
Items:

Attempts before depleting: 9
Catch Duration: 9 seconds
Items:

• Sum all the probabilities in the list
  
• Generate a random number between 0 and the summed up value
  
• If there is a fishing luck modifier: Multiply the random number with (1 - fishing luck modifier percentage)
  
• The reward will be the last item in the list where the random number is smaller than the sum of items probabilities up to (and including) that item's probability

Note: This means that having a fishing luck modifier will decrease the probability of the last item in the list, and increase the items' probabilities before it

1. No fishing luck modifier [194 * (1 - 0.0)]
   
   Item

   Probability

   Superior Salmon

   9.79%

   Red Herring

   43.81%

   Common Roach

   46.39%
2. 20% fishing luck modifier [194 * (1 - 0.20)]
   
   Item

   Probability

   Superior Salmon

   12.24%

   Red Herring

   54.77%

   Common Roach

   32.99%

To see the fishing spots, please refer to my other guide
point of interest guide
Or please refer to my DYSMANTLE interactive map[ogmods.github.io]