SANDPOINT — Phosphorus is an element that is naturally found in food and water, as well as living things.

It is, in fact, essential for life for the creation of DNA, cell membranes, bones and teeth, said Wyatt Mintken, a Clark Fork Junior High School student as he explained the importance of phosphorus to a group of Northside Elementary fifth graders during a field trip to the Pack River on Friday. Phosphorus ends up in the river through the process of “weathering,” he said, which occurs when a flowing river dissolves rock over time. Too much phosphorus, however, is harmful, Mintken said.

“When there are too many phosphates in the water it increases a process called eutrophication, which makes algae, and algae picks up dissolved oxygen from the water because it needs it to survive, but fish also need it to survive,” said CFJH student Ryan Matteson. “So when the algae takes the oxygen from the water, it can kill the fish because they don’t have any oxygen left.”

After telling the younger students about phosphorus, the Clark Fork students, with testing kit in hand, made their way to the water to get a sample of the water to later determine the phosphate levels of the Pack River.

CFHS science teacher Becky Haag, who leads the school’s outdoor experiential learning track, teamed up with Northside Elementary fifth-grade teacher Jeanne Warwick for the field trip. The 18 CFHS students and 22 Northside kids walked from the elementary school to the Pack River, where they split into four groups for each of the testing areas — pH, dissolved oxygen, phosphates and habitat.

CFHS students, who ranged from grade eight to 11, had done some research on each of the four testing areas as part of the focus with the outdoor track is natural resources. It was also an opportunity for them to teach their skills to younger students in a collaboration between the schools.

“I love doing this kind of thing with the other schools,” Haag said, adding that cross-curricular learning can help different subjects make more sense to the students. “So I like to bring the schools together, and the different disciplines, too.”

For Warwick’s fifth-grade class, all of their efforts so far this year will culminate in their Future City projects. Future City is a competition where students build virtual, and then scale models, of a city in accordance with the theme of the year. This year’s theme is “Tapping Into Clean Water,” so all of the science lessons for the class are centered around water, Warwick said.

“We’ve done a lot of investigating about ecosystems that revolve around water, so ponds, rivers, swamps, lakes, creeks, and we have done a lot of reading and learned how important a water source is to a local city,” Warwick said.

Warwick said the Pack River is an important resource, feeding into the valley where the school is located, all the way to the Pack River Delta where it meets Lake Pend Oreille. Because it passes so close to the school, she said it made a perfect spot for the kids to get some water quality education. The fifth-graders also took a trip to Lutherhaven in Coeur d’Alene, she said, where they learned about the watersheds in the Lake Coeur d’Alene area and how the lake is a main source for eagles. They will be going on an eagle cruise on Lake Coeur d’Alene in December as well. Another trip to give them insight on all things water will be to Albeni Falls Dam.

While the students can’t officially compete in the Future City competition this year, as it is designated for grades 6-8, the kids will have a school competition later in the school year.

Mary Malone can be reached by email at mmalone@bonnercountydailybee.com and follow her on Twitter @MaryDailyBee.