* CLEAN SWEEP: Kayaking whitewater brings to mind the line Lyle Lovett used to describe his brief marriage to Julia Roberts: "Even a blind chicken finds a few grains of corn now and then." The Potomac River, from Great Falls to Little Falls and beyond, for many is something great to walk along, drive over or ignore. But for paddlers it can be an essential and revealing place. When not surfing waves or holes, you can see herons and turkey vultures, snakes and hawks, but if you look closer you also can see constant reminders of human trespass: the pair of cotton underwear hanging from a high branch just above the Feeder Canal, the thrown-out condoms in the parking lot across from Old Angler's Inn, the shards of glass on mid-river islands, the soda and beer bottles floating in swirls and currents. It's clear the Potomac and its banks are part paradise and part dumping ground, and regularly need to be cared for. To that end, the Potomac Conservancy will host a river clean-up on Saturday starting at 9 a.m. on Roosevelt Island in Arlington. Volunteers are needed. Come dressed in work clothes and boots; gloves and trash bags will be provided. For more information, visit www.potomac.org.

Also on Saturday at 9 a.m. the Conservancy will help put on Growing Native Day, in which volunteers are needed to collect native hardwood tree seeds for planting in the Potomac Watershed. To sign up, contact Bryan Seipp at coordinator@growingnative.org. To learn more about other collection dates in the program, visit www.growingnative.org.

* WHO ARE YOU?: Bob Pickett, a naturalist with the Potomac Appalachian Trail Club, will present a talk titled "Appalachian Mammals" at REI's College Park store on Wednesday at 7 p.m. The free event, described as "a hands-on look at many of the 63 mammal species that can be encountered in the central and southern Appalachians," will touch upon the habits and habitats of "venomous shrews, rattlesnake-immune opossum, hybridizing coyotes and wolves, and non-hibernating black bear," and much else. For details, visit www.rei.com.

* KEEP MOVING, KEEP WARM: Hudson Trail Outfitters will host four more cross-country skiing clinics on Tuesday at its stores in Fairfax and Towson, Md., and on Oct. 26 at its stores at Tenley and Pentagon Row in Arlington. These will be followed by several "Dressing for Cold Weather" clinics at various stores on Nov. 2 and Nov. 9. All events start at 7 p.m. For details, visit www.hudsontrail.com.

-- John Mullen

mullenj@washpost.com