The water wars are raging again in America's heartland. Drought-stricken states are competing for the increasingly scarce water of the Missouri River and have taken their case to the White House.

Officials from more than 30 states have written President Barack Obama urging him to intervene - or not - in a dispute about whether water in the Missouri River's upstream reservoirs should be released to flow down to the Mississippi River.

Officeholders in downstream states say the water is needed to help raise low levels on the Mississippi that are threatening to halt barge traffic.

But if the water is released, officials in upstream states warn that the toll of the drought could worsen for farms and towns that depend on the Missouri River.