Even as a persistent drought strangles the Colorado River and threatens the viability of giant reservoirs and dams erected decades ago, Western states and local governments are eyeing more projects to tap the flow of the 1,450-mile river and its tributaries.

Whether those potential new reservoirs or other diversions would further tax an already overwhelmed system, or actually help states and municipalities adapt to a changing climate while making better use of their dwindling supplies, is a point of contention between environmentalists and water managers.