Rivers, lakes, ski slopes — often the best playgrounds in the county can be the riskiest for the skin.

Doctors are warning residents to mind their sun exposure this summer, especially since cancer data suggests Nevada County has one of the highest melanoma rates in Northern California.

“If you can catch it in the earliest stage, there's a 98 percent survival rate,” said Dr. Matthew Muellenhoff, dermatologist at SierraDerm in Grass Valley. But if the cancer progresses from the surface to the bloodstream, it's far worse.

Skin cancer is one of the few visible cancers, but people need to know how to recognize a suspicious skin spot from a harmless one. Moles that change, have asymmetrical shapes or unusual colors, are some of the biggest red flags.

“It's important to get people aware,” he said.

Muellenhoff, who has been practicing dermatology in Nevada County for the past six years, analyzed cancer data collected between 1999 and 2003 in 14 Northern California counties.

The county's melanoma rate during that time was 25 per 100,000, with a mortality rate of 3.4 deaths per 100,000.

“Considering the high number of elderly and Caucasians in Nevada County, it is not unreasonable to expect a higher incidence of melanoma over that of younger, mixed-race populations,” Muellenhoff wrote.

More alarming: He found the county has the third-highest incidence of invasive (deep tissue) melanoma, and the second highest mortality rate of the 14 Northern California counties, many with similar demographics.

There's no single factor that seems to be behind the elevated rates, but Muellenhoff says the lakes and ski resorts, where the sun's rays are reflected and intensified, may contribute.

Also, many seniors in the area grew up before sunscreen was commonplace.

“They were never told to protect themselves when they were younger,” Muellenhoff said. “That was an era when baby oil and iodine were accepted, and sunscreens weren't readily available.”

Now, they pay the consequences of sunbathing — in the form of skin cancer.

While some of the biggest risk factors — fair skin, moles, a family history — are unavoidable, sun exposure is. Muellenhoff recommends slathering up with an SPF 30 sunscreen year round, and keeping an eye out for suspicious moles.

“We're hoping we'll see a trend downward, with people being smarter in the sun,” he said.

To contact Staff Writer Michelle Rindels, e-mail mrindels@theunion.com or call (530) 477-4247.