Over the past 50 years, phosphorus (P) has been added each year to Lake 227, making it the world’s longest experiment in P fertilization. Located in Canada’s Experimental Lakes Area, Lake 227 conclusively demonstrated that excess phosphate in lakes causes algal blooms, in turn leading to worldwide bans on phosphates in detergents, improvements in wastewater P removal, and reductions in fertilizer applications. A key question, however, is: Where did the P added to Lake 227 end up? This is where David O’Connell and Philippe Van Cappellen of the Ecohydrology Research Group, together with colleagues from Canada, Netherlands, and USA, turned to examining phosphorus in the sediments accumulating at the bottom of the lake.