One million people were on the beach in June, July and August, said Imperial Beach Lifeguard Captain Robert Stabenow, compared to 1.4 million in 2010.
Numbers fluctuate every year and can decline for any number of reasons, but cooler than average weather is the the top determinant.
With low summer numbers, annual beach attendance will likely be below estimates at the start of the summer that .
"The numbers always correlate with the weather, and the past two years have been cooler and less sunny than in 2009," Lifeguard Captain Robert Stabenow said. "When we had that warm weather, we had almost 800 rescues and three million people."
The biggest days for beach attendance were during the U.S. Open Sandcastle Competition weekend when 385,000 people swelled the shores, to make up near 40 percent of summer beach attendance.
28,000 people came to the beach on the Fourth of July, the second largest day of beach attendance of the year.
Fewer people meant fewer rescues.
Through Labor Day, 272 rescues were made in 2011, compared to 427 last year.
Lifeguard Art Ayala said small waves, cool water and a change in local school schedules also played a role in fewer rescues.
54 people were rescued on the Fourth of July, more than any other day of the year and twice as many rescues as during the sandcastle competition weekend.
Rescue spikes are also hard to predict, Stabenow said. It is often assumed that rescues are highest when the waves are their biggest.
"Sometimes that large surf just pushes a lot of people onto beach but in three to six foot surf you get a lot of rescues, so it just depends," he said.
Annual Beach AttendanceYear Estimated Visitors Rescues 2010 2.6 million 512 2009 3.1 million 946 2008 2.3 million 785 2007 2.6 million 508 2006 2.9 million 687 2005 2 million 334
Source: U.S. Lifesaving Association