It has over 100 tributaries.

Its drainage basin covers 1/3 of the USA and some of Canada.

 Heavy rain in April 1993 saturated the upper basin so storms through June and July caused a large amount of surface run-off.

An area of land the size of Britain was flooded.

Road bridges had to be closed.

43 lives were lost and a lot of property was destroyed there were 50,000 evacuees.

Long term effects included the fact that the water didn't go away quickly and it was still draining off the land months later.

Sewage had been washed with the water so their was a great risk of disease.

It took moths to clean out houses and offices.

Stagnant water attracted mosquitoes and rats.

Human activity: dams, no water could penetrate through the soil because of buildings and concrete.

Reducing the risk of flooding:

Dams have been added to make large lakes.

Strengthen the levees.

Afforestation - trees are planted to slow down surface run-off.