Joe Guyen of Fairfax asks. How do you get to the point where Difficult Run enters the Potomac?

He wants to know because he's heard there is good smallmouth fishing there, and I can attest to that. It's a hard hike in, but worth the effort.

Take Rt. 193 north from the Beltway It's a windy road. Head west a few miles, then just beyond the entrance to Madeira School (which may not be marked) you'll go down a hill to a new concrete bridge. That bridge crosses Difficult Run, but instead of crossing, stop at the parking lot to the left, east of the bridge.

Park, walk across the bridge and look immediately right. There's a path, staying along the edge of the run most of the way, you'll finally hit the mouth.

"It's a rough but beautiful hike past waterfalls, over steep rocks. At the end is a sandy beach, then slightly upstream on the Potomac are some big boulders. We usually fish minnows around the boulders with good success.

The Virginia Institute of Marine Science has been awarded a $774,000 federal grant to study aquatic vegetation and the disappearance of eel grass from the Chesapeake Bay. The grass serving as nursery beds for much aquatic life, has been disappearin rapidly from the Bay in recent years. Many scientists feel the decline has a direct negative effect on fish and shellfish populations.

The Department of Interior has a new waterfowl identification field guide available for $180. It's called "Ducks at a Distance," and is available by writting Supt. of Documents, U.S. Government Printing Ofice, Washington Printing Office, Washington, D.C. 20240. The 52-page booklet has full-color illustrations by Fish and Wildlife Service artist BOb Hines.

The annual Children's Hospital benefit fishing tournament will be staged Saturday, July 29. Hours are 7 a.m. to 1 p.m., with $100 prize for the biggest fish caught. Entrance fee is $20 aboat and fishermen will ply the waters of fthe Chesapeake from Love Point to Sharps Island Light.

Proceeds go to Children's Hospital. Call 244-0300 to register. Entries close Friday.

The Potomac-Patuxent Chapter of Trout Unlimited will run a Potomac bass outing Aug. 5 from 2 p.m. to dark on waters near the West Virginia line. For information call 301 - 494-8281 or 301 - 897-8679.

The Optimist clubs of Charles County have scheduled their annual tractor pull Saturday at the Charles County Fair Grounds, Route 301 south of La Plata. It can be quite a spectacle, with bored, stroked and supercharged monsters strutting their stuff.

The bash starts at 11 a.m. The fee is $4 for adults, $1.50 for children 6-12, free for tots.

The Fish and Wildlife Service has announced that steel shot regulations for waterfowl hunters next year still will apply only to users of 12-gauge ammunition. The exception for non-12-gauge guns is slated to expire the following season, with shells for all gauges are expected to be available.

The Fish and Wildlife Service also announced that income from sales of fishing and hunting licenses set a record last year. The total was nearly $329 million, up $10 million over 1976, although the number of fish license holders actually declined, according to the agency.

Fishermen spent $156 million for licenses and hunters spent $172.8 million.

A total of 400,219 hunting licenses, tags, permits and stamps were issued in Maryland at a cost of $2,258,204. In Virginia 903,020 were issued for $4,239,094.

For fishing, 181,522 licenses, tags, permits and stamps were issued in Maryland for $701,548, and 725,725 were issued in Virginia for $2,461.149.