One sure harbinger of spring around my house isn't the crabgrass getting ready for its onslaught on my lawn or the birds chirping in the plum tree out in the back yard.

It's my offspring asking, "What's new at Lagoon this season?"Their interest in Lagoon is probably due to the fact that we live barely five miles from the popular resort and we drive past it every time we go into Salt Lake City, so the amusement park is a constant reminder that, when summer finally arrives - especially after a long, snowbound winter such as the one we just endured - Lagoon stands as a symbol of summertime fun.

So, what's new at Lagoon this season? Well, for the summer of 1989, Lagoon is planning to make a big splash - literally.

Remember Lagoon's famous swimming pool, filled with "water fit to drink"? It's being replaced by a $5 million water theme park with nine major water slides (in a variety of configurations), a roaring rapids innertube ride, a "lazy river" floating experience for those who are more laid-back, a children's pool packed with a number of aquatic adventures, and an adult pool complex with a gentle wave action and three hot tubs.

Keep in mind that when I first visited the site of this big, new project - formally called Lagoon-A-Beach - it looked more like a possible venue for Olympics Mud Wrestling. Where the old L-shaped pool and the now-razed locker rooms used to be were workers slogging around in the muck, trying to get caught up on a construction period that had been delayed by a longer-than-expected winter.

While the rides and other Lagoon activities will be open (Saturdays and Sundays only, beginning this weekend) the grand opening of Lagoon-A-Beach won't be until early in June.

Ron Van Woerden, director of Lagoon's entertainment division, said Lagoon-A-Beach is an integral part of the park's 10-year master plan.

According to this long-range calendar, for the 1990 season you'll probably see the park's namesake - the man-made lagoon - take on new emphasis. The tenative plans for the lake in the center of the park include changes in the wild animal compounds, with many of the animals being moved into more natural settings, and construction of a boardwalk along part of the lagoon to make it more pedestrian oriented. Also, instead of one train encircling Pioneer Village and another encircling the lagoon, the two sets of tracks will be joined for one long railroad excursion around both.

Other long-range plans include a tall-masted boat anchored toward the west side of the lagoon, where the high-divers and seals featured last season would perform. (They're not scheduled to appear during 1989 but should be back in their new surroundings in 1990.) Another possible attraction for 1990 would be a water-skiing exhibition on the lagoon.

Cyprus Gardens, eat your aquatic heart out.

Meanwhile, back at Lagoon-A-Beach, when I was visiting the site last month, worrying about whether or not some of the quagmire might really be quicksand, I was reminded of the classic western, "The Big Country," in which - at the finale - Gregory Peck and Jean Simmons, astride their horses, look from a Texas plateau across the banks of a river called the Big Muddy.

Several weeks ago, that's what Lagoon-A-Beach's lazy river looked like - the Big Muddy.

But Van Woerden assured me that, weather permitting, construction should proceed at a rapid pace. The slides themselves are prefabricated. Once the poles are imbedded and in place, it's just a matter of installing the tubes and sluices that make up the slides and serpentines.

When we called him a week or two later, he said the forms were in place for the concrete banks of the Lazy River. Work is also proceeding on a new ticket office and a beach house.

Patrons inside the amusement park itself who are walking from the Mother Goose Land area back to Pioneer Village will have a new raised deck for a viewing area, from which they'll be able to watch the swimmers enjoying the pools and slides.

There'll also be space in Lagoon-A-Beach for sunning and playing volleyball, for those who don't want to swim, float, splash, slide or soak.

Here's a preliminary glimpse at what the exotic Lagoon-A-Beach will have to offer:

- Three serpentine slides, twisting and turning along 1,200 feet of Fiberglass from a height of 56 feet.

- Two speed slides (one "freefall" and the other with a hump), from a height of 65 feet.

- Four enclosed "tube" style slides, attached to 31-foot towers.

- The "Lazy River" ride, with waterfalls, a "dancing waters" fountain, bridges, a section called the Snake River, a tunnel, some optional rapids (there'll be a fork in the stream, so you can opt for staying with the gentle flow or attacking the rapids) and a wave generator.

- The "Rapids River" ride, a wilder version of the lazy river, ridden on innertubes through a series of five horseshoe curves.

- An adult activity pool, featuring a gentle wave generator, three hot tubs and a refreshing "cascading waters" section.

- A fun-filled children's pool, where the water depth is no more than one foot, featuring tire swings, waterfalls, water bubblers, a rope bridge, a spectacular aquatic volcano (it spews water, not molten lava), a geyser fountain, tunnels and a variety of kiddy-oriented slides.

Other features of the Lagoon-A-Beach landscape will include a beach house/gift shop, an arcade, food service facilities, picnic terraces, a volleyball court and ample space for just lounging around.

The Lagoon-A-Beach site was designed by Leisure and Recreation Concepts Inc. (LARC), of Dallas, Texas.

(BU) ON LAGOON'S CALENDAR - For nearly eight weeks this summer (July 14 through Sept. 4), Lagoon will hold an 1890s-style "Pioneer Village Country Fair," sort of like an old-fashioned block party. There'll be a lumberjack show, with log rolling and ax throwing; the Guerrero Family high-wire balancing act (45 feet above the ground); a petting zoo with pioneer animals, an old-fashioned rainmaker (with guaranteed results), an ongoing barbecue adjacent to the Log Flume, and "Yes, Sir, That's My Baby," a revue featuring trained baby animals.

No celebrity-style concerts are on Lagoon's calendar this year, except for one day when KBER Radio will bring in some well-known performers.

Van Woerden said the Lagoon Stadium isn't suitable for concerts. Long-range plans call for a large amphitheater to be incorporated into the stadium area.

-THE LAGOON OPERA HOUSE will be utilized this summer for an independent production of "The Little Shop of Horrors."

According to Jeffry P. Belnap of Bountiful, a freelance special events producer, the show is tentatively scheduled to run June 21 through Sept. 2, Wednesdays through Saturdays, at 8:30 p.m.

The production is being directed by Edward J. Gryska of Salt Lake Acting Company, where the show had its regional premiere in 1986.