famous bodies of water. and that shouldn't be the case as abc's paul beaven reports. >> reporter: washington's national mall, a stunning showcase of american history. but these days, tourists strolling along the reflecting pool probably aren't humming "america the beautiful" that is unless they love algae. >> kind of gross, yeah. that's a little bit of a letdown. >> reporter: 'o beautiful for spacious skies -- waves of algae are spoiling the view. >> you don't get an image like this anywhere else. kind of a detraction. >> reporter: a slimy, smelly detraction that two years and $34 million in renovations were supposed to clear up. the water in the pool used to come from d.c.'s drinking supply. now a brand new pump and pipe system circulates water from the tidal basin and filters with ozone. the park service is calling this a break-in period. saying the new system just needs some fine-tuning.