In this activity, learners discuss the different salinities of oceans, rivers and estuaries. Learners then use experimentation to determine which sample is the best model of each type of natural water source. For the first test, learners make a hydrometer and use it to measure the density of the liquid samples. In the second test, learners freeze the water samples and examine them at certain time intervals to check degree of freezing, texture of the frozen samples, and other specifics that vary according to the amount of salt in the water. This activity can follow the Water Salinities I activity and/or be used in conjunction with the Estuaries activity, both of which can be found on SMILE.