The mud was found near a former Whitehall leather tannery site at the polluted lake.
Dredging is scheduled to take place from Sept. 12 through Oct. 10. A public meeting is planned for Tuesday about the effort.
The Muskegon Conservation District, working with state and federal environmental officials, discovered the discolored mud in the spring.
Similar purple sediment has been found during prior cleanup efforts, and likely is related to dye used at the former tannery site. The worst of White Lake's contamination stems from the days of leather-tanning operations and manufacturing chemicals.
White Lake been designated for special restoration efforts.