Credit Islands lies opposite the mouth of the Rock River and is connect to the Iowa shore at Davemport by a causeway across the head of Credit Island Slough. Half of Credit Islands has been developed, offering Davenport Residents a golf course and a bike trail. The rest is bottomland hardwood forest, a haven for birdwatchers. The downstream tips of the island collect sand and mud washed down from Black Hawk Creek, which empties into the slough. Emergent plants-duck potatoes, the most common form of arrowhead—have taken root in the muck. Songbirds love the seeds, waterfowl scavenge the tubers, muskrats and beavers eat the whole plant. Where it is deep enough, the slough offers over-wintering habitat for sport fish. Bluegill and crappie spawn in it. But there is more, Credit Island Slough and the other sloughs that meander through this shallow stretch of the Upper Mississippi are ideal for canoers and kayakers.
River Action, Inc is suggesting Credit Island Slough and others be turned into a canoe trail, with rental facilities on Credit Island. River Action, Inc. in the Quad Cities, has applied for a grant to set signs in the sloughs that border the Iowa bank of the Upper Mississippi.
This section of the Mississippi is new, 20,000 years new, formed by glacial floods in Illinoian and Wisconsinan times.
300,000 years ago, before the advance of the Illinoian ice sheet, the Mississippi flowed south of Rock Island, Illinois and turned east through the Princeton Bedrock Valley to meet the Ancient River Teays in central Illinois, formed the Mississippi-Illinois River, and flow south to its confluence with the Ancient Iowa-Cedar River.
Glacial floods created the Mississippi Gorge south of Rock Island, Illinois. During the Illinois stage of glaciation, ice repeatedly blocked the river’s flow into the Princeton Bedrock Valley where the river flowed east across Illinois to meet the Ancient River Teays and form the Illinois River. Glacial lakes formed behind the ice dams, filled with low-sediment water, hungry water, which when it spilled through its outlets carried enough power to erode the bedrock gorges between Andalusia, Illinois and Muscatine, Iowa, and between Cordova and Andalusia. The Illinoian glacier retreated and filled the newly carved gorges with sediment. The Mississippi returned to its ancient course.
The process repeated itself 20,000 yuears ago when the Michigan Lobe of the Wisconsinan glacier pushed west across the Princeton Bedrock Valley and Glacial Lake Milan pooled behind it. When the lake drained away, it reexcavated the two gorges. The retreat of the Michigan Lobe filled the Princeton Valley with drift and the Mississippi abandoned it ancient channel for its new channel, took over the channel of the Ancient Iowa-Cedar and flowed south to its confluence with the Illinois.
South of the Quad Cities, the river flattens and widens. Here, the river deposited sediment carried through the steep Port Byron Gorge, filling the Andalucia Gorge with narrow, lozenge-shaped islands, which occupy the center of the river. The sloughs that flow either side of the islands and through the islands are ideal for canoeing and kayaking.