There is a Master Plan (2015) for drinking water supply and waste water treatment in the Lake Atitlán basin, that includes new treatment plants and a giant sewage pipeline connecting all the towns that will export sewage out of the basin. Technically, the Master Plan is sound and if executed effectively it would save the lake. It draws on successful restoration efforts in Italy (Lake Bolsena and Lake Garda), Germany (Lake Constance), and the U.S.A (Lake Tahoe and Lake Washington). Read more about the Master Plan here.
The plan is controversial though. Implementation would entail all the challenges and complexities associated with large infrastructure projects in a corrupt, 3rd world country. Many environmentalists and indigenous groups do not believe the pipeline would be built with respect for the rights of indigenous communities, and they will continue to campaign against it. Also, the plan would require massive investment in a country where the majority of all budgets are lost to corruption. As of December 2016, of the 7 new treatment plants slated to be built in 2016, only 1 has been built. Commitment to implementation appears to be low.
This is a long term plan, with no guarantee that it can be implemented effectively before it is too late to save Lake Atitlán. Thus, we must press ahead urgently with other remediation efforts.