Does algae ever build up in water lines?

In the 6 years that I've owned our IG pool, I've only "lost" the water to algae twice during the summer and only twice have I opened the pool in the Spring to find green water. I've always had no problem at all getting rid of the algae by shocking with bleach and scrubbing the walls but I have wondered if the algae tends to build up inside the underground water lines since those lines never get scrubbed. Is this possible source of algae and is there any way to periodically clean the lines to ensure they are clear?

Lots of bleach.

Algae is a plant. Unless light can get into your plumbing, no algae can grow there.