The invaders, named and gated: zebra mussels in the basin, carp at the gate and not through it

USGS NONINDIGENOUS AQUATIC SPECIES RECORD · AS OF NOVEMBER 2026

The invasive record for this ground divides cleanly into a presence and a watch, and the article keeps them divided. The presence is the zebra mussel, Dreissena polymorpha, recorded in the U.S. Geological Survey's Nonindigenous Aquatic Species database for the St. Joseph River basin and measured in the basin's own science: Bobeldyk and colleagues (Écoscience, 2005) assessed zebra mussel populations across the coupled lake-stream systems of this basin — Indiana and Michigan water — in 2000 and 2003, and found the pattern that governs the invasion here: densities highest in the invaded lakes and falling downstream of them, the basin's streams seeded again and again from their lakes, a source-and-sink system in which a connected lake is a mussel factory for the water below it. The mussel is therefore established in this basin's lakes and the streams they feed — the county's ground included at basin size — filter-feeding the same water Chapman's sixteen ducks swam. One disambiguation prints with emphasis, because the press record invites the error: the widely reported 2009 finding of a zebra mussel "in the St. Joseph River at Fort Wayne" concerns the other St. Joseph River — the Maumee-basin river of Allen County, which shares this river's name and nothing else — and does not belong in this ground's record. The watch is the carp: bighead and silver carp are not established in any Great Lake, on the Michigan DNR's record, and the state watches this river for them by name — Michigan's invasive-carp programme monitors the St. Joseph and the Kalamazoo as key congregation waters, with environmental-DNA surveillance, precisely because a Lake Michigan river with this one's flow is a door the fish would use. Behind the door the front stands far off: the Illinois Waterway's established front for large invasive carp sits in the Dresden Island Pool, some 76 kilometres downstream of Lake Michigan on the 2025 inter-agency record, and young silver carp were found in the Marseilles Pool in August 2026, some eighty miles from the lake — movement, watched, and still two locks-and-lakes away from this river's mouth. So the carp entry for Granger's record is a gate status, not a presence: as of November 2026 no invasive carp stands in the St. Joseph River of Michigan and Indiana, none in Lake Michigan, and the state's surveillance names this river as watched. Named, gated, and dated — the mussel in, the carp out and monitored — is the whole of the honest invasive record.

Sources:

1. U.S. Geological Survey, Nonindigenous Aquatic Species database: zebra mussel (Dreissena polymorpha) recorded for the St. Joseph River basin.
2. Bobeldyk et al. (2005), Écoscience: zebra mussel populations assessed 2000 and 2003 in coupled lake-stream systems of the St. Joseph River basin (Indiana and Michigan); downstream decline from invaded lakes; source–sink model.
3. Michigan Department of Natural Resources, invasive carp record: bighead and silver carp not established in any Great Lake; active monitoring, with eDNA surveillance, of the St. Joseph and Kalamazoo rivers as key congregation locations.
4. Invasive Carp Regional Coordinating Committee, 2025 Interim Summary: the large-fish invasion front in the Dresden Island Pool, ~76 km downstream of Lake Michigan; young silver carp in the Marseilles Pool, August 2026, ~80 miles from the lake.