Grass Carp Ctenopharyngodon idella was imported to the United States in the 1960s for research into its usefulness as a biocontrol agent for nuisance aquatic vegetation. Escapees and intentionally stocked individuals founded wild, spawning populations in the Mississippi River and tributaries to the Laurentian Great Lakes. USGS-led research on the Sandusky River, a tributary to Lake Erie, demonstrated spawning of Grass Carp in 2015. In 2018, sampling with ichthyoplankton nets in the Sandusky River 11-13 June produced thousands of suspected fertilized Grass Carp eggs. Genetic analysis of 49 eggs identified by microscopic analysis as Grass Carp eggs confirmed all were from Grass Carp, demonstrating 100% accuracy of microscopic analysis. These data include the development stages of the eggs, along with the DNA sequences of a select subset of eggs. We used published keys to estimate developmental stage of eggs, which can be used in conjunction with hydraulic models to predict spawning and hatching locations and with genetic analyses to estimate numbers of spawning adults. First release: December 2018 Revised: August 2019 (ver. 2.0) Revised: July 2020 (ver. 3.0)