The gelatinous globs of the bacteria grow on the iron that is precipitated out of the water. Iron is very sensitive to REDOX potential. Anytime water is oxygenated there is the potential to form a precipitate. One way the iron precipitate occurs is by the oxygenation of groundwater. It can also happen in other ways.

Groundwater is a good example because it contains little or no oxygen and for this reason is commonly saturated or even supersaturated with iron. All it takes is a little oxygen and a precipate will occur as everyone has seen on porcelain sinks and toilets. Pond water though it contains some concentration of oxygen, could also form a precipitate should additional aeration occur (as water leaks from through the dam).

When my pond draws down, the iron contained in the sediments is oxidized during periods of low water (when sediments are exposed to air). It's not noticeable when its dry but when the water level comes back up, there will be a 1-2' wide orange ring that is visible just above the low water mark (visible right now).

I'm not sure if the orange bacteria can be used to determine the source of the seepage at your dam just by its presence or absence. If a groundwater sample, pond water sample and seepage water sample were collected and analyzed, it would be possible to model the source of the seepage by the water chemistry. A tracer might be used.