Illinois
River, 2 miles below Havana to 1.5 miles below the Head of Grand Island
The conditions in this stretch of river are better than those found north of Havana. For the first time below Chillicothe, Richardson finds the nymphs of the common willow-fly thriving, as well as the common sand-caddis, Hydropsyche sp. The mollusks do not decline in this stretch as they had from Chillicothe to above Havana. The snails, however, do experience a 95% reduction in poundage between 1913-15 and 1920. Table 9 shows that the impacts to snail species are less in this stretch of the river than for the other two sections discussed.
Table 9: Snail Fauna of Bottom Muds Below Havana, 1913-15 to 1920 (Richardson 1920)
| Family | Species |
| I Species Surviving in 1920 | |
| Viviparidae | Campeloma subsolidum |
| Pleuroceridae | Pleurocera sp |
| Sphaeriidae | Musculium transversum |
| II Species present in 1913-1915 but not found in 1920 | |
| Viviparidae | Lioplax subcarinata |
| Vivipara contectoides | |
| Vivipara subpurpurea | |
| Pleuroceridae | Goniobasis sp |
| Amnicolidae | Amnicola emarginata |
| Amnicola sp. | |
| Sphaeriidae | Sphaerium stamineum |
| Ancyclidae | Ancylus sp. |
Table 10 illustrates Richardson’s findings that the impacts to the bottom fauna are not as severe below Havana as it is for the two other sections discussed.
Table 10: All Small Bottom-Animals from Havana to Grand Island, 1913-15 to 1920 (Richardson 1920)
| Channel | 4-7 ft zone | 1-3 ft. zone | ||||
| 1915 | 1920 | 1915 | 1920 | 1915 | 1920 | |
| Viviparidae and Pleuroceridae | 6 | 10 | 73 | 9 | 99 | 104 |
| Sphaeriidae | 6 | 2 | 84 | 12 | 89 | 12 |
| Amnicolidae, Valvatidae, etc. | 0 | 0 | 4 | 0 | 2 | 0 |
| Chironomidae | Trace | 36 | 2 | 170 | 6 | 244 |
| Oligochaeta | 0.5 | 2 | 9 | 33 | 0 | 24 |
| Other insects, worms, Crustacea, etc. | 3 | 78 | 20 | 27 | 12 | 429 |
| Grand Total | 15 | 128 | 192 | 251 | 208 | 813 |
