We apologize to anyone who found himself on the waterfront yesterday or today looking for one of the tall ships and craving a hot dog. "Riverfest '85" is to take place next weekend, contrary to what you read in this space yesterday. The dates are June 8 and 9.

LEST WE FORGET in the wake of recent concern about drownings, there are friendlier sections of the Potomac River than the dangerous waters between Chain Bridge and Great Falls. And one is right along the Maine Avenue Waterfront, where the Potomac is certifiably cleaner than it has been in years -- and where a fine weekend festival gets under way today to celebrate the progress. Billed as "Riverfest '85," the events are intended to combine waterside fun with an appreciation of how much the years of cooperation between governments of the region have been able to accomplish in the way of a river cleanup.

When President Johnson first spoke out for making the Potomac River a national model, most people knew it was a tall order. But today you're talking tall ships, sailing in much cleaner waters, thanks in large part to better sewage treatment at the Blue Plains plant. The U.S. Geological Survey has reported that there have "significant reductions" in organic carbon and phosphorus in the river, though the growth of algae continues to be a problem.

In any event, today's fete is not a swimming party. In addition to the appearance of nearly a dozen tall ships, there will be boats -- including a paddle-wheel cruise to greet Jacques Cousteau's "Calypso" and one to watch the fireworks and grand finale on Sunday evening. Arts, crafts and ethnic foods have been promised as well. If last year's celebration is any indicator, this weekend's should be a success.

Then, perhaps, the same kind of concentration that has gone into improving the river can be directed to improving the riverside -- especially to bringing more life to the Maine Avenue shores. We continue to believe that with good planning and mixed uses, Washington's waterfront could rival any along the East Coast (are you ready, Harborplace fans?) as an attraction for tourists and residents alike. See what you think this weekend.