Chhath is also about cleanliness and caring for rivers ponds, lakes and canals where the prayers are offered.
Links:
[1] http://admin.indiaenvironmentportal.org.in/news/future-tense-water-pollution-forces-people-celebrate-indoor-chhath
[2] http://admin.indiaenvironmentportal.org.in/category/newspaper/daily-news-analysis-delhi
[3] http://admin.indiaenvironmentportal.org.in/category/thesaurus/uttar-pradesh
[4] http://admin.indiaenvironmentportal.org.in/category/thesaurus/water-pollution
[5] http://admin.indiaenvironmentportal.org.in/category/thesaurus/chhath-puja
[6] http://admin.indiaenvironmentportal.org.in/category/thesaurus/religious-beliefs
[7] http://admin.indiaenvironmentportal.org.in/category/thesaurus/yamuna