Volunteers for Catch the King, Guinness Book-recognized as the world’s largest citizen-science project, completed their fourth year of flood tide measurements on Sunday.

Nearly 160 volunteers, from Girl Scouts to senior citizens, walked along riverbanks, coastal bays and creeks from Virginia Beach to the far northern reaches of the Potomac River, mapping nearly 25,000 high-water marks during 2020’s highest astronomical tide.

The turnout was higher than expected. Catch the King organizers had decided early this year to not publicize or actively recruit new volunteers, due to the coronavirus pandemic. Yet, eager new participants found their way to the project. Among them were numerous Virginia Master Naturalists, especially from the Middle Peninsula, as well as Virginia Master Gardeners from the Northern Neck and 24 girls representing the Girl Scout Council of the Colonial Coast. Virginia Beach and Norfolk had big turnouts of veteran mappers as well.

“Despite the COVID restrict...