GORILLA HYDRILLA:

The monster vegetation some feared would eventually choke the Potomac is conspicuous by its absence again this year.

The Metropolitan Council of Governments reports that submerged aquatic grasses (SAGs) in the river from the District to Mount Vernon are below recent averages for the second straight year, evidently because of a cool, wet spring.

Hydrilla and its fellow grasses -- milfoil, coontail, stargrass, wigeon grass, etc. -- were thick around Washington during summers throughout most of the 1980s, spawning a boomlet in waterfowl and aquatic life.

Overall, total area of SAGs in the river is up to about 5,000 acres and still increasing, said COG's Giselle Bernstein, who keeps records. But the biggest concentrations this year are around Mallows Bay and Cherry Hill on the lower river, she said.

Bernstein said mowing operations to clear boat paths in heavily infested areas will begin later this month.

STOP AT 10:

Saltwater fishermen in Virginia and the tidal Potomac now must obey a 10-bluefish-a-day creel limit. The limit went into effect July 1; Maryland is expected to have a similar rule shortly.

The limit comes just as blues finally have arrived in the Bay in significant numbers. Doug Scheible aboard the headboat Bay King out of Ridge, Md., reports big catches of small blues in the one-pound range. He's mostly fishing in Maryland waters where there is no creel limit yet, though he said blues aplenty are in the Potomac around Point Lookout too.

TRAIL BENEFIT:

Famed mountaineer Lou Whittaker will emcee a slide show and auction to benefit Potomac Appalachian Trail Club at 7 p.m. Thursday at Stuart High School, Falls Church. A $3 donation is requested, proceeds going to PATC. Call 835-0740.

'SHROOMERS:

The Mycological Association of Washington is having its annual campout this weekend at the Summit near Mathias, W.Va., where members will be gobbling wild mushrooms as fast as they can be snipped, identified and cooked. For information write Buddy Kilpatrick at 2375 N. Edgewood St., Arlington, Va. 22207.