Fishing

Credit for this system belongs to reddit user u/NefariousNautilus who posted it to the r/DnDBehindTheScreen on 6/11/2021

Catching Fish - The Basics

First, The DM determines which table the fisherman will catch from and that player rolls 1d20.

Freshwater Fish Table

D20	Size	Type	Weight	Modifier
1	Small	Snackerel	1d4-1	+0
2	Small	Daggerfish	1d4	+1
3	Small	Mousegill	1d4+1	+1
4	Small	Red Trout	1d4+2	+2
5	Small	Whitefin	1d4+3	+2
6	Medium	Magefin Chub	2d4-1	+2
7	Medium	Starscale Trout	2d4	+3
8	Medium	Bluegill Minnowpike	2d4+1	+3
9	Medium	Owlbear Salmon	2d4+2	+4
10	Medium	Rapier Sturgeon	2d4+3	+4
11	Large	Mithril Carp	3d4-1	+4
12	Large	Tigerstripe Bass	3d4	+5
13	Large	Swordtooth Herring	3d4+1	+5
14	Large	Oarfish	3d4+2	+6
15	Large	Dragontail Pike	3d4+3	+6
16	Massive	Boatcutter Gar	4d4-1	+6
17	Massive	Lakesail	4d4	+7
18	Massive	Axehead Trout	4d4+1	+7
19	Massive	Whalefin	4d4+2	+8
20	Massive	Bearfish	4d4+3	+8

Saltwater Fish Table

D20	Size	Type	Weight	Modifier
1	Tiny	An Old Shoe	1d6-1	+0
2	Massive	Giant Squid	30d6+5	+7
3	Large	Mammoth Tuna	10d6+5	+6
4	Medium	Guildfin Grouper	5d6+3	+5
5	Enormous	Claymorefish	40d6+5	+8
6	Small	Trapjaw Snapper	3d6+3	+4
7	Medium	Nine-Tail Clubfish	6d6+2	+5
8	Large	Sealance	10d6+4	+6
9	Medium	Infidian Mackeral	4d6+2	+5
10	Small	Wolfhead Bass	2d6	+4
11	Medium	Kawahai	3d6+8	+5
12	Large	Crimson Steenbras	10d6+5	+6
13	Medium	Whitegill Rook	4d6+3	+5
14	Massive	Chimera Shark	40d6+5	+7
15	Tiny	Pearleye Anchovie	1d6-2	+0
16	Small	Silverpage Crevalle	2d6-2	+4
17	Medium	Onyxfin Bulltrout	4d6+3	+5
18	Large	Sultanfish	8d6+15	+6
19	Enormous	Seahir	35d6+10	+8
20	Titanic	Whaboleth	50d6+5	+9

The challenge is to get the fish from where it is hooked (20 ft away) to the boat/dock, where it can be pulled in.
Each round, the player and fish face off with a contested roll to see if the fish moves further or closer, in increments of 10 ft.

• If the player wins a contested roll, the fish moves 10 ft closer.
• If the fish wins, the fish moves 10 ft further.
• On ties, the fish stays put.
• Repeat the contested rolls until the fish is caught or escapes (0ft / 40ft)

For each contested roll, the DM rolls for the fish (adding the modifier from the table), while the player rolls whatever skill they can reasonably justify to the DM. The fish gets tired as the battle rages on, gaining a cumulative -1 penalty on each turn after the first.

Fish Traits

Not all fish are created equal, and some may possess unique traits that make them more difficult to catch.

• Desperate: Once per battle, the fish can make a desperate maneuver, gaining advantage on its next roll, but disadvantage on the following roll
• Brutal: The fish automatically wins on a 19 or 20
• Tireless: The fish is in particularly good shape, and the -1 penalty only accumulates every other round
• Sly Fish: Once per battle, the fish can re-roll its check AFTER seeing the player's roll
• Momentous Mover: Once per battle, the first time the fish wins a round, it moves 20ft away instead of 10ft
• Jumping Fish: Once per battle, after losing a round, instead of being reeled in 10 ft., the fish jumps out of the water and halts progress, staying in the same place

Legendary Fish

Every fisherman has a story of the one that got away. Most of these tavern tales are nothing more than lies, and spun yarns, but occasionally a fisherman does encounter a mysterious and rare creature among the waterways of the world. These fish may be exceptional in their size, their strength, or for other, more curious reasons. If you have reached an area that contains a legendary fish the DM may secretly roll a die to determine if it makes an appearance, but some of these fish may require special tackle, or lures to be produced.