Course
A USATF-certified, fast and flat course circling Grosse Ile, an island in the Detroit River. The half marathon and 15K start at Grosse Ile Middle School and the 5K at the Grosse Ile Naval Hangar, running on quiet island roads with river views throughout.
Key dates
- !RegistrationOpen now
- ★Race daySun 21 Mar 2027
About
The Rock CF Rivers Half Marathon is our signature spring event—uniting runners, walkers, families, and fighters to push limits and fuel hope. Every step supports the mission of Rock CF: to improve the quality of life for those living with cystic fibrosis through fitness, advocacy, and action.
Save Rock CF Rivers Half Marathon & 5K to your season and RunCalendar reminds you the morning entries open and before they close. Free on iPhone, no account needed.
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Bay City St. Patrick's Day Races
A festive Michigan tradition ranked among the nations top spring races
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IRONDOG 5k
Dog-friendly 5K funding MSU's emergency vet care
A confirmed date shows its day; a provisional one shows only its month, because we won't claim a day we don't have. This page is rebuilt every night from the RunCalendar catalogue.