Ground water flows from areas along the coastline and discharges directly to Lake Michigan. Under natural (pre-pumping) conditions, a much smaller regional component of discharge moved from as far away as the Waukesha area toward the Lake. Some of this regional ground water flow discharged at the Lake Michigan shore, some moved under the Lake to discharge farther east:

Model output: West-to-east sections showing locations and regional ground-water flow lines to Lake Blue formation is Maquoketa shale. Yellow formation is St. Peter sandstone. East of divide all flow lines go from water table toward Lake Michigan. (source: D.T. Feinstein, U.S. Geological Survey)

As pumping developed, the shallow ground-water discharge along the coastline diminished slightly while the regional flow pattern reversed.

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