A trident is a powerful weapon added to the 1.13 aquatic update. This guide will let you know how to find a Trident in Minecraft.
The only way to obtain them is to kill drowned mobs underwater. There is a 15% chance in bedrock and a 6.25% chance in the java edition of a drowning holding a trident.
Once you find one with a trident, it has an 8.5% chance of dropping a trident.
And with looting III, it becomes an 11.5% chance.
You can search rivers, but using an ocean biome to find the drowned is recommended.
Drinking a night vision potion will also make spotting them a lot easier.