One component of the Maryland School Performance Assessment; Program (MSPAP) is the state's performance-based assessments, criterion-referenced tests that require students to apply what they know and can do to solve problems and display other higher-order thinking skills. This document helps parents, teachers, students, and other citizens understand the tasks of the MSPAP. "Salinity" is a science and language usage task for fifth graders, one of nine tasks selected to demonstrate the MSPAP. Actual operational task materials are presented. The "Answer Book" contains questions and directions for students and space for students to record their answers. The task is an investigation of how a hydrometer can be used to measure the different levels of saltiness in water samples. A group of four students constructs a hydrometer and uses it to test water samples. Answers are recorded individually. The "Resource Book" contains a map of the Chesapeake Bay, and the "Examiner's Manual" contains instructor preparation activities and directions for students. (SLD)