After more than 15 years in the city, the Naperville Women’s Triathlon is being replaced this year with co-ed 10K and 5K running races. Participation in the Naperville women’s triathlon, and the triathlon sport as a whole, has declined over the years. Registration for the Naperville women’s triathlon peaked near 2,200 participants around 2007 and 2008 but fell to about 700 registered for the 2018 event, said Nick Lynch, president and CEO of 10xEM, which runs the event.