Bach, 76, is listed in serious condition at Harborview Medical Center in Seattle, where he was airlifted after the crash.
San Juan County Sheriff Rob Nou says Bach was trying to land on a grass airstrip Friday afternoon when he caught power lines with his landing gear as he neared the runway.
The plane landed upside-down in a field about two miles west of Friday Harbor.
His son, James Bach, told The Associated Press that his father was on his way to visit a friend on San Juan Island on Friday when his amphibian plane clipped a power line during landing, and crashed.
James Bach says his father, who was flying alone, suffered a head injury and broken shoulder.
"Right now we're waiting for the sedation to wear off, for him to fully wake up," the son said Saturday morning.
Bach is widely known as the author of the hugely popular 1970s best-seller "Jonathan Livingston Seagull," which sold more than 1 million copies in 1972 alone. The book contained fewer than 10,000 words, yet it broke all hard-cover sales records since "Gone with the Wind," according to Wikipedia.
In the book, published in 1970, Bach writes of a philosophically minded seagull seeking to rise above the flock, which is focused on the dull regimen of finding food scraps. Jonathan is banished from the group only to come upon more enlightened gulls who guide him to spiritual lessons, which Jonathan then imparts to others.
The short, simply crafted book gained little to no critical attention upon publication, but rose to No. 1 for several weeks on the New York Times bestseller list, and Bach quickly drew a loyal following.
In 1973, the book was turned into a movie, "Jonathan Livingston Seagull," produced by Paramount Pictures. The movie included a soundtrack by Neil Diamond.
Bach, who claims to be a direct descendant of Johann Sebastian Bach, has been a pilot for his adult life, often touching on his experience in the cockpit of his beloved plane in his writings.
Besides "Seagull," his other popular works include "Illusions: The Adventures of a Reluctant Messiah," a mystical story of a Midwestern barnstorming pilot's quest for self-discovery.
He often links the practice of flying to themes of a deeper spiritual quest.
"Dad described his religion as flying. He's a very avid aviator," James Bach said. "It would be terrible if he recovers and can't fly again - this guy needs to fly."
At the time of the crash, he was flying a 2008 Easton Gilbert G SEAREY aircraft that he nicknamed "Puff."
The National Transportation Safety Board and the Federal Aviation Administration are investigating the crash.