Strange lump on my pond goldfish

[Lorraine 45]

I have just noticed a lump on my gold fishes side can anyone help me with what it is and if it can be treated please images below

 

[Autumnsky]

Have you tested the water for ammonia, nitrite or nitrate? If you have these in unsafe levels it would be a good start to treat the water for that.

You might need to do some vac'ing, scooping, reducing excess decaying leaves, muck if it is there. Some water change. Not sure how you do maintenance on your pond.

From the pic, I cannot tell what it is.

Getting the water quality in a safe zone is one of the first line measures to help sick fish.

 

[Autumnsky]

Can you describe it, does more than one fish have it?

Common problems are fish Herpes, also Carp pox, and another common strain.

It seemed much larger than this - breeding starts /spots

Lymphocystis/Cauliflower Disease

but it seems big, and it could be a tumor.