Three distinct zones are found in each of the navigation 
pools. The upper end remains essentially in a normal open-river 
condition. Here original, natural water levels have not been 
altered to any great extent, marsh development is limited, and 
the natural condition of deep sloughs and wooded ialands is 
prevalent. In the middle zone of each pool, the dams have backed 
water over islands and old hay meadows, spreading water out over 
large, comparatively shallow areas. It is in this portion that 
the best marsh development has occurred. In the lower ends of 
the pool, immediately above each dam, water is impounded to a depth 
which often precludes marsh development. While this portion is 
essentially deep water, good aquatic plant growth has occurred in 
many instances, although true marsh development is limited. 
Prior to impoundment by the dams, timber was cleared to a 
contour 3 feet above the expected normal pool level. In all the 
pools most of the timber was cleared. Clearing and subsequent 
flooding made wide areas of former timberland available for marsh 
development and aquatic growth. 
Following impoundment in what is now the Upper Mississippi 
Refuge, important aquatic plant beds developed, and at present 
vast quantities of valuable waterfowl food and cover plants 
occur. So diversified are the aquatics that it is not unusual 
to find more than two dozen species in a matter of minutes any- 
where in the better marshes. 
Excellent growths of bulrush, burreed, sagittaria, and 
wildrice abound, with the rice increasing each year that water 
levels are favorable. Wildrice is of great importance not only 
as food and cover for ducks, but also as concealment for hunters. 
Twelve species of pondweeds form the bulk of the valuable water- 
fowl food on the Upper Mississippi Refuge. Wildcelery is in- 
creasing annually and is now locally abundant over much of the 
area, 
Comparatively little field feeding occurs on the Upper 
Mississippi Refuge north of the Wisconsin River, perhaps because 
there is sufficient natural food produced in the marshes to 
support the waterfowl populations using the area. South of the 
Wisconsin River, field feeding does occur, ‘become more and more 
important progressively down river. This could be due part to 
the arrival of ducks from the northwest where they have been | 
accustomed to field feeding as well as to the decrease in natural 
aquatic foods. 
As a matter of general interest, it should be pointed out 
that except for pool 13 where there is some scull-boat hunting, 
most hunting on the Upper Mississippi Refuge is normally 
