Just because water is nearby doesn't mean you have infrastructure to make use of it. For example the great lakes region has had droughts before that affected agriculture. This might surprise you because on a map, there is a huge body of freshwater to draw from nearby. However, to draw from that body, one needs to build pumping infrastructure sufficient to draw from it and to have this infrastructure go to where it needs to be, likely inland uphill from the great lakes requiring more pumping and reservoirs and other infrastructure. Reservoirs in particular are often dependent on having good natural conditions. It also needs to be overbuilt such to work in a drought, and therefore most of its costs will be wasted in times when its not needed. All of this costs money and political will to improve things, both of which the great lakes region is short of in recent history.