It is generally safe to feed some types of lettuce to turtles in moderation. However, not all types of lettuce are suitable for turtles. Iceberg lettuce, for example, has very low nutritional value and is not recommended for turtles. Instead, dark, leafy greens like romaine lettuce, red leaf lettuce, and green leaf lettuce are better options for feeding turtles. Always remember to wash the lettuce thoroughly and remove any uneaten portions from the enclosure to maintain cleanliness.