If you motor nine miles up the Patuxent River from the Chesapeake Bay - past slivers of beach and osprey nests - you'll pass a yellow buoy.
It isn't on the navigational maps, and it doesn't mark a crab pot, but it is probably one of the more expensive items moored in the river.
It's a weather buoy operated by the University of Maryland's Chesapeake Biological Laboratory. Every 15 minutes it sends data that is received by the lab and ultimately sent to a Web site where bay watchers can track subtle changes in water temperature, clarity, salinity and oxygen content.
Anglers use the information to try to deduce where the fish might be. Higher salinity levels could mean more ocean fish, and lower levels could mean that river fish will move further south. Low oxygen levels will mean no fish.
Windsurfers and kayakers check the water temperature and wind direction before venturing out.
It's a needy buoy. Lines dangle below it like tentacles on a jellyfish. As instruments monitor the bay, barnacles, algae, sea squirts and other maritime critters affix themselves to parts of the buoy, making the scientific readings less accurate.
So every two weeks, Tim Koles and Dean A. Chigounis - technicians with the biological lab - speed up the river in a motorboat, remove instruments so that they can be scrubbed down and take readings to determine the accuracy of the buoy's data.
The buoy appears to be a vulnerable and delicate machine, but it isn't. Stripped of its instruments, it stayed firmly anchored to the bay's floor during Tropical Storm Isabel.
Koles says he has been kicking himself for doubting the buoy then and removing the instruments during that storm.
"The next hurricane or tropical storm that comes through, [the instruments] will be there," he says.
The data that could be gathered from such a storm, Koles says, would be astounding.
When Koles started working with the buoy three years ago, it wasn't set up to relay data continuously. It was supposed to be a roving buoy, a station that could be moved easily to hot spots of algae activity.
But it has evolved into a fixture. It only comes out of the water for a few winter months, for servicing and a new paint job.
Koles has a love for setting up technology. At one point he showed off what is essentially a security camera pointed at a large osprey nest. People around the world view the Web site, and Koles worries that his e-mail inbox will begin to overflow because chicks haven't yet hatched.
Aboard the boat, it is all business. Changing the instruments takes about an hour. Koles and Chigounis have a pretty set routine.
They tie the buoy to the side of the motorboat and start yanking in the SONDEs, the long plastic cylinders that hold data-gathering instruments.
Chigounis guesses that each SONDE costs about $13,000. He ties one to a rope and prepares to throw it overboard.
"I think they are insured, but I don't want to be the guy [who] has to ask," Chigounis says. "That's why I triple-check that everything is secure."
The buoy is part of a growing network of coastal weather buoys that feed information to a central location.
The hope is that the network will become an on-the-water version of the National Oceanic and Atmospheric Administration's land-based weather system.
The buoy is also outfitted so that it can easily accept new sensors. It has 18 measuring devices attached to it, but Mario N. Tamburri, a professor at the Chesapeake Biology Laboratory who is in charge the buoy, would like to add current-reading devices.
Because of its adaptability, the buoy is used to test new types of sensors. Tamburri wouldn't say how much the buoy costs to operate but says his lab has a budget of $3.5 million that is divvied among projects.
The basic function of the buoy is to provide data about the water.
On the boat, Koles removes sea water, pours it into a plastic beaker and hands it to Chigounis.
"I'll take this back in our little lab - my makeshift lab," Chigounis says.
He squats in the cabin and puts the water though a filter so that only the sediment remains. The filter is removed, wrapped in tin foil and stored in a cooler. When he returns to shore, he will analyze it and compare it with others in the lab.
The weather's unpredictability is the point of the weather buoy. And 20 minutes into the buoy checkup, a squall line forms on the horizon.
Koles looks at the sky, puzzled. He had checked the radar, and the skies appeared to be clear.
The two scientists retreat to the cabin while a downpour pounds the boat.
In the cabin, Chigounis sighs. "Ah, the joys of monitoring a buoy," he says.