Usually orange water indicates a buildup of tannins on the water, caused by leaves, etc. Do you have oak trees near the pond? Do you have a lot of debris/leaves in the bottom?

I have no solution. However, ademink, I think while tannin is a common answer to brown colored water, considering the obvious intense orange colored particles shown in the micrograph, it is an unreasonable answer here.

Tannin can also cause orange water so I thought it was a reasonable answer. I apologize for being unreasonable.

Well I doubt many on here will recognize those microorganisms to tell you what you have in the water.

I found this after a quick google search:

"Sometimes other colors such as orange and reddish colors are noted on ponds. These events are usually caused by another type of algae called euglena. These
algae turn red or orange upon flowering and are unaffected by pond dyes
and cannot be controlled by chemicals once they turn red. A steady dose of copper products should be applied early in the season and continued all the way through the season."

I guess the algae might be what you see in the microscope. That would explain why it is here this year but not last year. It's just a growth of this kind of algae this year. Give it a try and let us know.

Another possible answer was that the pond is getting too much iron somehow.