All things considered, August should be a gosh-awful month for fishing. Heat, humidity, the sudden thunderstorms -- all figure strongly in the usual put-downs of the eighth month. But then no one could have guessed that recent days of dry, cool nights would perk up all matters piscatorial.

To wit: The bluefish of Chesapeake Bay are making a strong showing in some quarters. Okay, they're not the biggest we've seen, but they're blue and wild about trolled, cast or baited lures. Even in freshwater lakes and rivers, the bass are not as sluggish as they should be.

Then along comes the local angling duo of John Shelly and Frank Rinaldi, two youngsters who scoff at tales of poor flounder fishing at Ocean City, Maryland. The boys drifted minnow-baited bottom rigs in the backwaters between 25th and 33rd streets for several days last week. Each outing produced stringers of two-pounders. Again, not giants, but big enough to fill mother's kitchen with delectable odors of freshly fried fillets. MARYLAND RIVERS AND LAKES POTOMAC RIVER -- Get set for next Friday's start of the WJLA TV-7 fishing derby. The contest runs from August 27 through September 5 and all hands are invited. Fish anywhere between Cabin John and Wilson Bridge, from shore or boats, and enter your catches either at Fletcher's Boathouse, the Tidal Basin paddle boat center or at the Maine Avenue waterfront. There are prizes galore for young and old. If thundershowers don't mess things up, the catfish are biting throughout the river, from western sectors clear to Indianhead. The bass have been good to waders and boaters around Shepherdstown, West Virginia, Knoxville, Montgomery County and the District at Washington Channel, Roosevelt Island and the Spoils area near Wilson Bridge. WSSC RESERVOIRS -- Deep-fished plastic worms can do a number on the largemouths at Triadelphia and Rocky Gorge if you get there during the cool hours. One Rocky Gorge five-pounder was scored earlier this week on a surface buzzer in a deepwater cove. Small sunfish and crappies are plentiful around the brushpiles. DEEP CREEK LAKE -- A nine-pound-plus northern pike headed last week's fishing contest. Scattered hefty walleyes are taken on drifted curly-tailed jigs. Crankbaits and plastic worms are luring a few bass around landpoints. SUSQUEHANNA RIVER -- Surface buzz baits, such as the Lunker Lure, have drawn stripers and largemouth bass over structured areas inside the Flats and up to the dam. Conowingo Lake turns up catfish of note and occasional keeper bass and crappies. CHESTER RIVER -- Eastern Shore boaters use bottom rigs baited with clam snouts or bloodworms to catch fat white perch and a few large spot from inside Love Point into the river mouth. PATUXENT RIVER -- Ken Lamb of Lexington Park's Tacklebox shop tells of fine spot catches in the Hog Point area, where scattered sea trout and flounder have also taken up stations. But forget the Clark's Landing area of the river. We tried it twice last week with one guaranteed result: scads of tiny spot and loads of bluefish that were definitely too little to be away from their mothers. SOUTHERN MARYLAND LAKES -- Gilbert Run Park lake (Route 6, east of LaPLata) still shows willing sunfish in deep holes. Catfish are a bit harder to find for some reason. St. Mary's Lake (Camp Cosoma Road, off Route 5 near Leonardtown) is quickly becoming a faithful angler's friend with large sunfish and plenty of willing, if not always legal, bass. I tried Mann's new Electric Grape Augertail worm there the other day and boated 39 bass. Not bad, eh? PRETTYBOY RESERVOIR -- This beauty north of Baltimore has been giving up a smorgasbord of smallmouth and largemouth bass and crappies. Of course, live minnows always work, but plastic worms catch a fair share, too. NANTICOKE RIVER -- The river around Sharptown and the tributaries, Marshyhope Creek at Federalsburg and Broad Creek at Laurel, Delaware, have been fine for mixtures of largemouth bass, crappies and some rockfish. Talk about exitement. Try throwing a broken-back Rebel into the grassy shore when the tide is ebbing and watch the swirls behind the lure. CHESAPEAKE BAY Here's hoping a sudden heat spell won't slow down the action. Lots of trolling boaters have been happy with new arrivals of snapper bluefish plus a few lunker blues that are still around. Main trolling and chumming producers point to the Middlegrounds, Buoy 50 to Buoy 54, Tangier Sound, a stretch of dropoff water near Point Lookout, and Hooper's Island Light up to Sharp's Island and Stone Rock. Nighttimers on Point Lookout State Park's beaches occasionally find blues inhaling cut baits. Buoy 54, by the way, is still worth a night trip for peeler-crab baiters after sea trout. So is the Stone Rock area near the mouth of the Choptank. Clam snouts, bloodworms or grass shrimp (if you can get them) attract white perch around the pilings of Chesapeake Bay bridges. A few pan-sized rockfish are around there also. Eastern Bay and Bloody Point offers small breaking bluefish from time to time. In all, the fishing is pretty good considering it's August. VIRGINIA RIVERS AND LAKES SMITH MOUNTAIN LAKE -- Deep-fished live bait (minnows or sunfish) has attracted good numbers of striped bass. Trolled long-lipped lures also find the stripers during the dark hours. Largemouth bass, too, have been active, preferring black and purple plastic worms. LAKE GASTON -- Late afternoons and early mornings can be productive for the plastic-worm or deep-crankbait user. Local bass hunters say they've seen a marked improvement here and hope the hot, sticky weather will stay away. KERR RESERVOIR -- Buoys 4 to 6 above the dam have been hotspots for striper trolling. Bucktails, mostly in white, work well when dressed with a strip of white curly porkrind or plastic worm. Brushpiles and landpoints around Nutbush Creek were good striper-jigging areas last week. RAPPAHANNOCK RIVER -- It all depends on local thundershowers. If they stay away, an early- morning wading trip around the Rapidan junction would definitely produce smallmouth bass on spinners or live minnows and hellgramites. The Fredericksburg sector is always good for catfish and scattered bass, with downstream tidal sectors showing fair bassing when river begins to ebb. LAKE ANNA -- Cool nights had brought bass closer to shore, some into four-foot levels where plastic worms did the job. Now, however, the deeper- structured water may have to be searched again. Catfish and sunnies are very willing on baits. OCCOQUAN RESERVOIR -- Recent cool nights turned on northern pike, bass and smaller panfish. A number of pike and bass were weighed in at Fountainhead Park. Bottom-fished nightcrawlers are fine for channel cats. CHICKAHOMINY RIVER -- Bass simply love plastic grubs or worms. Crappies are about and go for minnows or gardenworms. Catfish are plentiful. In the lake by the same name, the sunfish are turned on, but bass catches are down. BACK BAY -- Knotts Island area at the Carolina border has been good to bass hounds casting Beetlespins, Johnson Silver Minnows and plastic worms. Of course, you must pick your spots and times of day. Those who are stubborn enough to stick with it will come home with trophy bass. OCEAN AND INLETS MARYLAND -- Twelve-year-olds Frank Rinaldi and John Shelly love to spend vacations at Ocean City. The two spend more time fishing than anything else and their bulging catches of up to two-pound flounder are nothing to sneer at. The boys drifted minnows last week between 25th and 33d streets in the back bay waters, as bloodworm bait. VIRGINIA -- Remember our report that flounder fishing at Chincoteague was the best (for August) in many a year? Now comes local flounder angler Harry Bink who called to say, "True, but you forgot to mention how tiny the flounder are." Bink complained loudly about the pesky little ones, too small to keep. We'll stick to our story. Fish in deep holes, hold a good drift and you'll eventually find doormats big enough to bring home not only at Chincoteague, but also at Wachapreague, Oyster and Metomkin on the Eastern Shore. Offshore bluewater trollers will find wahoo, amberjack, billfish and bottom-fished seabass. Inside the mouth of Chesapeake Bay, at the Bay-Bridge Tunnel islands, you'll find a few sea trout and flounder. Bluefish and spot will be the main fare of western bay shore fishermen.