This Data Nugget begins with a phenomenon: a salt marsh ecosystem in Gloucester, MA, was changed when a road restricted tidal flow between the salt marsh and the ocean. In 2003, a culvert was constructed that restored tidal flow under the road. Scientists want to know whether the culvert has improved the health of the salt marsh ecosystem. Using counts of mummichogs, a small fish species, to indicate the health of the salt marsh, data was collected both before and after tidal flow was restored. Using the data, students are asked to answer the driving scientific question: “What effect did the removal of the tidal restrictions have on the number of mummichogs found upstream?” The lesson involves calculating averages, graphing data, making a claim, and providing evidence and reasoning to support the claim. Students are also asked to suggest questions to be investigated next. A teacher guide, student activity sheets (provided at three different proficiency levels), a presentation, a grading rubric, and additional supports and information are provided.