Sick Goldfish with one side of its face swollen

[Lms5057]

Hi!
We are relatively new (2 years in) to having fish. We inherited the pond when we moved into our house. We usually have the pond professionally opened and closed, but the old owner walked us through doing it ourselves a couple times. We have only encountered a sick fish once before and had a company come and check the pond.
Tonight I noticed a fish laying on the rocky ledge of the pond, not moving. I went to check to see if he was alive and he swam away, staying close to the top of the water and away from all of his friends. It appears that one side of his face/lips are swollen or distended. Does anyone have any ideas what this could be?
Thank you for your time!

 

[j.w]

@Lms5057
Hard to say what is wrong w/o seeing it up close and I am not too knowledgeable on fish disease's. Does it look like an injury? Could also be a tumor.

 

[Lms5057]

Thank you for your reply! Even looking at him up close, it just looks like the left side of his cheek is larger than the right. No injury or discoloration.
I gave him a salt bath this morning and added stress coat to the pond. Hoping he improves over the next few days.

 

[Mmathis]

How big is your pond and how many fish do you have?

When you say that you have the pond professionally opened and closed....what exactly do you mean?

 

[addy1]

Do you have honey bees around? Also wasps? They drink from the ponds, the fish might have tried to make a snack of one. My bees are in the ponds constantly but mainly in the plant filled fishless ponds