News media is notoriously poor at digesting and presenting research. Here's one recent paper based on actual research. It says what I said, that the St. Clair dredging has had a small contribution to lowering Huron/Michigan:
"The Study Board concluded that:
1. The difference in water levels between Lake Michigan-Huron and Lake Erie has declined by about 23 centimetres (cm) (9 inches) between 1963 (following the last major navigational channel dredging in the St. Clair River) and 2006.
2. Three key factors contributed to this 23 cm (9 inches) change:
- A change in the conveyance (water-carrying capacity) of the St. Clair River accounts for an estimated 7 to 14 cm (2.8 to 5.5 inches) of the decline.
- Glacial isostatic adjustment (the uneven shifts of the earth’s crust since the last period of continental glaciations ended) accounts for about 4 to 5 cm (1.6 to 2.0 inches) of the fall.
- Changes in climatic patterns account for 9 to 17 cm (3.5 to 6.7 inches); this factor has become even more important in recent years, accounting for an estimated 58 to 76 percent of the decline between 1996 and 2005.
3. There has been no significant erosion of the channel along the length of the St. Clair River bed since at least 2000. Based on survey data collected in 1971, there appears to have been some enlargement of the channel between 1971 and 2000. However, the changes in the channel are within the error of the surveys. In addition, there are issues regarding the reliability of the 1971 data."
Perhaps there is more recent research on the subject. If so, please post the link (to the paper, not to media reports).