For many New York students, studying the Hudson River is as natural as walking outside.

The Hudson passes through dozens of diverse towns and cities on its 315-mile run from the heights of Mt. Marcy, where it starts at Lake Tear of the Clouds, to New York City.

To mark the 400th anniversary of Henry Hudson's discovery of the river that bears his name, educators, environmentalists and activists have developed programs and educational curricula to celebrate the river as a rich learning resource.

For example, the Henry Hudson 400 New York, a nonprofit foundation whose goal is to connect history to the future, put together a USA-Netherlands exhibit of rare maps and documents at South Street Seaport in lower Manhattan.

The maps depict 17th-century exploration, early Dutch settlements in New York and the Atlantic trade that made Manhattan into a business and cultural mecca.

Also on display for the first time in the United States is the document showing the purchase of Manhattan.

"New Amsterdam: The Island at the Center of the World" can be seen until Jan. 2.

At www.hudson400.com, the rare maps are overlaid with contemporary Google maps of the area, charting courses of Hudson's four voyages. The site shows 3-D models of Hudson's ship, the Half Moon, and illustrates climate change through the years.

Atlantic Ocean tides surge up the river from New York City harbor all the way to Troy — site of one of three summer professional development science and math programs for educators connecting the river and the classroom.

This SENSE IT program is delivered through Beacon Institute For Rivers and Estuaries (www.bire.org), Clarkson University, and a $1.4 million grant from the National Science Foundation.

Educators in the programs learned during an intensive two weeks how to build sensors, and, in turn, teach students how to build and use them. The sensors monitor the Hudson's water temperature, a factor affecting the health of plants, animals and organisms.

The teachers will meet during the school year, and again next summer, to learn how to build other types of sensors.

The program's goal, said Liesl Hotaling, chief education officer for Beacon Institute, is to "help replenish the K-12 science, technology, engineering and math education in this country."

Now that school is back in session, SENSE IT educators are teaching students the lessons necessary to build the sensors and program them. A few students from each school attended the second part of the training. This fall they will help teachers inform all students how to monitor water temperatures.

"It was the best thing I did all summer," said Anne Green of the Hadley-Luzerne Teachers Association, who regularly takes students to the nearby river for lessons.

"This program allows classroom teachers to participate in real-life scientific research that will have a lasting environmental impact, and that they will be able to pass on to their students," said NYSUT President Dick Iannuzzi.

Learning to build river sensors gave teachers plenty of summer homework. The sensors will allow for continuous monitoring, "not just discrete sampling," Green said.

Teachers also learned how to write computer programs, which they downloaded into Lego NXT processors, hand-held computer-like devices. The NXTs were fitted with two wires — one connected to the sensor, and one to a thermoster that is dropped into the water. This takes the temperature that is then recorded on the NXT.

"There's a lot of math in this," said Green, who is an environmental science teacher. Canoeing, fishing and rafting lure people to the North Country community all summer."Our economy is based on tourism," Green said. "Water quality is a big part of it."

Farther downriver, a massive and often controversial Environmental Protection Agency dredging project is under way at Fort Edward to clear the river of PCBs from industry waste.

Many plants and mills once located at the water's edge dumped tons of waste into the river. Environmentalists are still concerned about some ongoing practices.

"When we do a unit on the environment, I use the dredging project as a positive and negative impact of technology," said Mark Belden, Schuylerville Teachers Association member and SENSE IT teacher.

"We study the invention of PCBs as a huge asset to the electrical insulation industry, and then how they were misused and dumped in the river," Belden said.

The sensor project, he said, fits into classroom study about the river that runs past their Saratoga County town. Connecting a real-life project to state standards can improve student achievement.

The sensor, tool kits and NXT processors provided are a "huge" boost to get students interested in electronics, Belden said.

The students he brought to the second week of instruction "were texting their buddies, telling them how cool this is," he said.

Belden, meanwhile, is networking with professors at the state's engineering colleges to find out what skill base they want students to have.

Downstate, the river is wider and busier with large powerboats, ships and barges transporting goods, and sailboats.

Carol Slotkin, a NYSUT Board member from Sullivan County, notified union locals along the river about the sensor project, urging them to apply.

"This will enrich students and build on what they know," she said. "It's an excellent example of school and community partnerships."

"It's a great way to engage teachers and students in learning within their own environment," said NYSUT Vice President Maria Neira.

Poughkeepsie sent living environment and integrated algebra teachers to the professional development program, and the local union, the Poughkeepsie Public School TA, worked with administrators to allow the pair to team-teach the sensor project class.

"It really puts engineering, science, computers, math and technology all in one," said Amber Kardas, middle-level math teacher who divides the work with colleague Gregg Farris.

Nearby Beacon is a small city where educators often pan the river for riches.

Legendary folk singer Pete Seeger, who helped found the educational and environmental sloop Clearwater, performs in the schools, said Kim Atwell, president of the Beacon TA. Sending high school physics teacher Sheryl Hawks to the river watch program was a natural.

The entire program, which continues through next year, is 120 hours of professional development, said the Beacon Institute's Hotaling, who will visit each educator's class this school year.

Upcoming projects include building senors for conductivity, turbidity and pressure/depth.

"We're hoping to create a citizen science program out of this," Hotaling said.