From the shady deck of a pontoon boat on the Patuxent River near Croom, Mother Nature doesn’t look under siege.

A great blue heron flaps by over the sun-dappled deep green water; a late-season osprey swoops low over the marsh bordering the river channel; pickerel weed blooms in purple spikes against the green riot at the river’s edge.

But there are problems in this paradise, as Matt Felperin, a park naturalist at Patuxent River Park, pointed out Saturday during the Journey into Jug Bay’s Past tour of the river and the historic Mount Calvert home beside it.

Felperin explained that wild rice — yes, the same kind that Grandma may have served at Thanksgiving dinner — is an important food source for birds, including red-winged blackbirds and migratory Canada geese, but that the introduction of nonmigratory Canada geese — which have a different feeding pattern — put some pressure on the resource.

“Jug bay has the highest density of wild rice in Maryland,” Felperin said, but it is threatened by the nonmigratory geese, which are “pretty much river cows. They eat several pounds of vegetation a day, and really tear up the rice.”

The problem is that the migratory geese have adapted to having the wild rice available to feed on during their annual journey. But now, “they get here when it’s gone,” Felperin said. Park staff try to control the greedy nonmigratory geese, blocking goose access to stands of wild rice with low fences that look ludicrously unprepared to stop something that flies. Felperin said the fences don’t allow geese enough room to land on the water next to the rice, since they need a good distance to lose speed on the water.

Park staff are also working to boost the wood duck population with nesting boxes at the water’s edge, mimicking their natural tree-cavity nest sites. The boxes, 4 or 5 feet above the surface, make it a bit easier for the ducklings than their natural nests.

“They naturally nest in tree cavities up to 100 feet above the ground,” Felperin told the handful of passengers on the tour. “They lay up to 10 eggs, because the young leave the nest 24 hours after they’re hatched, and they jump out. They can’t fly. They jump out and land on the forest floor. They only weigh about an ounce, so when they spread their feet and their stubby wings, they slow down enough. They are really easy pickings for foxes and raccoons,” when they first land.

At Mount Calvert, a brick plantation house built in the 1780s or ’90s, Kristin Montaperto, the assistant archaeology program manager with the county Parks and Recreation Division, gave a brief rundown of the history of the site — from ancient woodland American Indians whose traces date back 8,000 years, through an early period as the county seat, then as the site of the plantation house and associated buildings.

The house has been restored, though the second and third floors are not sturdy enough for visitors, and the first floor houses a small museum with displays on archaeological findings at the site over the years.

Montaperto pointed out a working archaeological site on the property, which she said archaeologists think may have been slaves’ quarters during the period when slavery was legal and a key part of the economy of the region. The site is open on Saturdays through the end of October, though it may close during special events, and residents are welcome to come and watch the archaeologists work and ask questions.

On the way back to the dock at Patuxent River Park, Felperin stopped for an impromptu water quality check, letting the lone child aboard handle the Secchi disk, a round piece of wood divided into alternating black and white quarters. Felperin explained that the disk is used to gauge the amount of sediment in the water.

The depth at which the disk disappears gives a data point scientists can use to measure the rise and fall of particles in the water. Saturday, the disk was visible for about a meter below the surface, an exceptionally good measurement.

“My colleagues will definitely want to hear about this,” Felperin said with a big smile.

Maybe Mother Nature hasn’t lost after all.