This episode is nearly identical in title, plot, and even some camera angles to the Bonanza (1959) episode "A Matter Of Circumstance" (which only switched the focus to Michael Landon's character rather than Karen Grassle's); both were directed by William Claxton.
In one scene Mary appears to be afraid of the water, asking if it's too deep. However, in the episode "Remember Me" earlier in the season, Mary is not afraid as she and Laura jump into a lake to rescue a group of abandoned pups.