THE INVASION has begun. The blues have arrived in big numbers at Point Lookout, even though the Chesapeake Bay water temperature has been a chilly 57 degrees.

When the surface temperature hits 62 degrees, the blues will go wild and eat anything within range. In fact, one angler already reports taking them on short sections of broom handle rigged with a screw eye on the front and a treble hook firmly anchored on the back. He claims the fish don't care -- just as long as it's moving fast and splashing lots of water.

On another front, white perch have been showing up in good numbers in sheltered rivers and coves, but you need a boat to reach them. Most are concentrated in the deeper holes where they are feeding on grass shrimp and minnows. WHAT'S THE CATCH? WASHINGTON & VICINITY

POTOMAC RIVER -- You can cash in on a catfish tournament being held by Ray Fletcher at Fletcher's Landing. The tournament, which began last weekend and runs until June 30, covers catfish caught in the Potomac between Key Bridge and Little Falls. The entry fee is $3; cash prizes based on the number of entries will be awarded for the three largest catfish caught.

Anglers have been hooking up with some good-sized white perch, crappies, hickory shad and catfish on a variety of baits and lures from shore. The river level has been higher and the current stronger than normal because of recent rains, making it unsafe for boaters.

Down by the Woodrow Wilson Bridge, the shallow waters near the Spoils Area have been good for largemouths caught on cast spinner baits, plastic worms and crankbaits.

Ken Penrod of Outdoor Life Unlimited in Beltsville reports the tidal Potomac has come alive with largemouths. He says one of his parties caught 13 bass, of which the heaviest was five pounds, seven ounces. Bass guide Ken Wilson reports one of his parties bagged 17 bass on the same day.

A bit farther upriver, anglers fishing the Washington Channel have been loading up on good numbers of largemouths and some huge catfish. Overall, fishing conditions in the river are now considered excellent. MARYLAND

TRIADELPHIA & ROCKY GORGE -- Bass fishing has really taken off during the past few days at both Washington Suburban Sanitary Commission lakes. Bob Griffith at Fishing and Archery Outfitters in Laurel checked in several largemouths last weekend that weighed more than five pounds. Thomas Perkins of Laurel hooked up with a five-pound, two-ouncer while fishing with a spinner bait. Columbia resident James Lowell hooked a largemouth weighing more than five pounds using a live minnow. A slammer northern pike measuring 32 inches long and weighing 7 pounds, 12 ounces was taken by Charles Clark of Laurel, and a huge bluegill of more than a pound was caught by Clarence Dennett, also of Laurel. VIRGINIA

LAKE ANNA -- Sturgeon Creek Marina in Spotsylvania is having a bass tournament on Sunday. Check-in time is 6 a.m. at the marina; the entry fee is $40 dollars per boat. Cash prizes will be awarded based on the number of entries. The bass fishing here has been running hot and cold for the past few days because of the weather, says John Jones of the marina.

Anna Point Marina, also in Spotsylvania, is having its grand opening celebration this weekend, holding a fishing rodeo on Saturday and Sunday with proceeds going to the American Cancer Society. Redskin coaches Charlie Taylor and Don Breaux are supposed to be on hand Saturday to kick off the event.

NEW RIVER -- Lacey All at All's Hunting and Fishing in Salem reports he has checked in a new state record smallmouth bass at seven pounds, six ounces. Larry Reynolds of Salem caught it on white spinner bait with a four-inch chartreuse grub hooked to the back end of the lure.

SMITH MOUNTAIN LAKE -- Bass fishing has been picking up, with the largemouths moving into the docks during the late evening. Crankbaits are taking both largemouth and smallmouths up to four pounds. Striper fishing has dropped off a bit because of the cold snap but is expected to improve by the first week in May.

RAPPAHANNOCK RIVER -- The shad run is peaking with the arrival of the American shad last week, says Carl Gentry at Chesley's Sporting Goods in Fredericksburg. However, he says smallmouth bass fishing has been red hot. Live minnows have been best for the bass; the shad are taking darts fished in fast water. CHESAPEAKE BAY

SUSQUEHANNA RIVER -- Three days of torrential rain forced the opening of 10 flood gates at Conowingo Dam, reports Terry Rhudy at Conowingo Bait in Darlington, and churned the river to a sea of mud. The muddy water has driven the larger white perch back to the Susquehanna Flats until the water once again runs clear.

SUSQUEHANNA FLATS -- The muddy water coming down the Susquehanna curtailed most of the fishing here this past week, according to Herb Benjamin at Herb's Tackle Shop in North East. Normally you would expect to see good numbers of largemouths showing up in the shallow water preparing to spawn. However, the decrease in water temperature coupled with muddy water has pushed the bass back to deeper areas.

DUNDEE AND GUNPOWDER RIVERS -- The white perch are still hitting well at the mouth of the Dundee and Seneca rivers. Sue Demaf at Gunpowder Bait and Tackle in Essex says several of her customers have been hooking large females using grass shrimp fished on the bottom. Catfish are in the same area and taking nightcrawlers fished in the deeper holes. Tidewater bass fishing has dropped off a bit because of the colder water.

BALTIMORE METROPOLITAN AREA -- Although the perch have yet to appear in the Key Bridge and Curtis Creek areas, it will take only a slight warming trend to bring them into the shallows. This should happen within the next week or two, according to Clyde's Sport Shop in Baltimore. The tidal ponds at Belgrove Road have been turned into a sea of mud by the recent rains. Before the storm, some good-sized catfish and perch were being taken in this easily accessible area by shorebound anglers using grass shrimp and nightcrawlers.

BAY BRIDGE AREA -- White perch fishing is still holding up well in the Magothy and Severn rivers, according to the Angler's Sport Center on U.S. 50 in Annapolis. The deep holes in the middle and upper reaches of the rivers are most productive for the larger spawners. Grass shrimp and live minnows fished close to the bottom have been producing the better catches. If the weather warms, you could see the first bluefish caught in the Bay Bridge area of the Chesapeake by this weekend. Large silver and white spoons trolled in 25 to 35 feet of water should be productive.

SOLOMONS ISLAND -- Blues are now at the mouth of the Patuxent, reports Captain Bill Meadows on the El Toro, and the few charters that have been working the area have been loading up on choppers weighing up to 19 pounds. Chumming has been the best method to take the blues.

Alex Lavish of Lexington Park hooked the first bluefish of the 1986 season -- a 16-pound, 12-ounce chopper that won a $120 fishing outfit from Ken Lamb at The Tackle Box in Lexington Park. Lamb reports the blue was taken from the pier at the Patuxent Naval Air Station on cut bait. Several large blues and an occasional sea trout come from this particular area each year.

POINT LOOKOUT -- Schools of huge chopper blues are now congregated at the mouth of the Potomac, and the first charter boat on the scene was Captain Eddie Davis' Edith Rose. Davis reported loading up on huge blues weighing nearly 20 pounds while chumming near the mouth of the river. Captain Bruce Scheible at Scheible's Fishing Center says his boats loaded up on huge chopper blues weighing up to 18 pounds while chumming with ground menhaden. Scheible said the blues are not concentrated in any given area, but there were enough of them that every boat managed to hook up with enough fish to fill their coolers.

CAPE CHARLES -- Believe it or not, smaller blues have already arrived at the tip of the Delmarva Penninsula. Captain Otis Asal on the Bucaneer reports catching several five- to seven-pound blues while fishing above Kings Creek Marina.

Captain Monty Webb of Eastern Shore Safaris reports tau-tog are still plentiful just out from Cape Charles Harbor and they're taking chunks of crab fished on the bottom. Larger blues are still lingering at the mouth of the Chesapeake near the bridge tunnel complex, but the rough conditions made fishing for them nearly impossible last weekend. Sea trout are still showing up in the nets and should be hitting bucktails jigged close to the bridge structure. However, the winds will have to drop considerably for small boat anglers to work the pilings. ATLANTIC OCEAN

QUIMBY, VA. -- Although the mackerel have vanished from the offshore waters, the big news here is that the first of the summer flounder have arrived in the shallow back bays. Several anglers near Virginia Landing caught some huge flounder weighing up to 13 pounds. The average, however, has been three to four pounds. Live minnows and squid strips fished on the bottom have accounted for the better catches.

WACHAPREAGUE -- Scattered catches of flounder have been in the channels between the islands. Live minnows and squid strips have produced best. The larger fish seem to be concentrated in the deeper water, but as the weather warms, they'll migrate into the shallows. OCEAN CITY -- Captain Coleman Bunting reports a few boats have been venturing out to take on bluefish migrating up the coast. Blues weighing up to 10 pounds were caught last weekend by anglers fishing for the remnants of the mackerel, which are now off central New Jersey. CASTING COMPETITION

The Dupont Company, manufacturer of Stren fishing line, is holding its annual Long Casting Tournament this weekend at Cape Henlopen State Park in Lewes, Del. Qualifying trials are Friday from 3 to 6 p.m. and Saturday at 9 a.m. The competition itself begins Saturday at 10 a.m. and continues through Sunday. Minimum casting distance is 450 feet in order to qualify. It's free to watch, free to enter and very competitive. The top ten casters will receive merchandise and cash awards. The first-place winner will win a free trip to the national tournament June 6 in Harrisburg, Pa.