The reservation and some surrounding communities get their drinking water from the Missouri River. For the past seven years, severe drought conditions has resulted in very low water levels on the Missouri River lakes - so low, in fact, that water has become more valuable than gold or oil.
If a solution isn't found soon, 14,000 residents on the reservation and surrounding area will be looking for new sources of water this year.
The intake pipe for the water system that is set in the Cheyenne River at its confluence with the Missouri River has been moved into deeper water once, but is now filling with silt.
''You've heard of the two-headed monster? Well, ours has three heads,'' said Harold Frazier, chairman of the Cheyenne River Sioux Tribe.
''It will affect Indians and non-Indians, on-reservation and off-reservation communities. It is a drought emergency and an environmental emergency,'' he said.
Frazier said the silt now filling the intake pipe is laden with arsenic, heavy metals and mercury.
''We face a crisis this summer that is unimaginable,'' Frazier said.
Eventually the 40 patients on dialysis will be affected, and the fear is that many people who have limited water access will collect contaminated water wherever they can find it and diseases such as dysentery, cholera and parasites will occur.
The situation has become serious enough to bring in the entire congressional delegation from South Dakota. Senators Tim Johnson, Democrat, and Republican John Thune, and Democrat Rep. Stephanie Herseth, are working together to leverage pressure on government agencies to come up with a solution.
The congressional delegation has required the U.S. Army Corps of Engineers to find a solution to help the reservation and communities, and that any expenses come from Emergency Preparedness and Disaster Response.
The Army Corps plans to spend $6 million to move the water pipe intake further into the Missouri River on the Mni Waste water system that serves 17 communities and the Cheyenne River Reservation.
''I am pleased that the U.S. Army Corps of Engineers has recognized the urgency of this situation, and is moving to ensure communities in South Dakota are not left without water,'' Herseth noted in a statement. ''This action is clearly necessary.
''However, the solution is decidedly short-term, and the delegation must work with the Corps, the state, local and tribal governments, and other federal agencies to craft a permanent solution to the problem of low water levels in the Missouri River in South Dakota.''
The Cheyenne River Sioux Tribe has a boundary on the western shoreline of the Missouri River on what is now named Lake Oahe. The lakes and pools were created when the earthen dams were completed in the late 1950s and early 1960s. Vast amounts of land were flooded by the huge reservoirs that are not only used as water sources, but as recreation resources that bring in millions of dollars to the economy of South Dakota and the reservations.
The Standing Rock Sioux Tribe, located to the north of Cheyenne River, is experiencing the same situation. Tribal and state officials have repeatedly asked the Army Corps to solve the problem of low reservoir levels.
The Standing Rock Sioux Tribe has also had to extend the intake pipe further into the river as the water reseeds from the shorelines. Boating docks have been closed and others moved to reach the water, and most can be seen as if in dry dock along the river's banks.
South Dakota Gov. Mike Rounds has asked the Army Corps to maintain water levels by shutting down the flow - which would create navigational problems for the states below South Dakota.
Army Corps officials have stated that next year, navigation in the lower Missouri may not exist.
The situation is so drastic that 157 new applicants for water have been denied and more than 200 homes that are planned by the Cheyenne River Housing Authority will be denied service by the Mni Waste water system.
Drought conditions have also contributed to dry grasslands, raising the threat of fires; and with little water, the ability to fight those potential fires is questionable. In fact, wastewater from a lagoon was used to extinguish one fire.
Ranchers have had to haul water great distances for livestock - a costly solution - and many have sold off large numbers of their breeding stock.
A new hospital and nursing home are planned for construction on Cheyenne River, but no water will be supplied to either if the problem is not resolved.
An estimate from the Army Corps stated that the water level could end up 31 feet below normal by the end of summer. There was no snow pack in the watershed areas of the Rocky Mountains, Wyoming and Montana. That snow pack is crucial to supplying runoff to the Missouri River. None of the river's tributaries, either in North or South Dakota, is flowing at normal levels.
The flow into Lake Oahe is 20 percent of normal, said Mike Swenson, Army Corps hydrological engineer.
He said the current level of Lake Oahe is just two feet over the lowest level ever recorded.
''Our last basic simulation showed it dropping to about a little above 1,567 feet [seven feeet less than the current level],'' Swenson said. Because of the low levels, the hydroelectric output of the dams is nearly one-half of normal.
''This is a more serious problem that what people think, and we need to deal with it,'' said John McGinness, Dewey County commissioner. Part of Dewey County is located on the Cheyenne Reservation.
''We simply can't wait any longer or these communities won't survive,'' said Eagle Butte Mayor John Bachman.