This lack of water in streams isn't only because of low rainfall. With less snowpack, there was less meltwater this spring to feed rivers and streams. Look at the illustration above. The water table is the top of the underground area where water fills the pores and cracks in the soil or rock. The surface of a stream or pond is an extension of that water table.
Water is free to flow from the surface underground and vice-versa.
This relationship between surface water and groundwater makes water use during droughts very tricky. If streams are lower than normal, groundwater flows out to temporarily keep the streams flowing. But soon the groundwater becomes depleted to the point where the water table drops and the stream dries up. Over pumping of groundwater from wells can cause water from streams to get sucked into the ground, drying up the streams. Many towns and farms get their water by pumping groundwater from wells.