A boat or recreational vehicle ladder apparatus is provided. One aspect of the present ladder apparatus includes an elongated extension handle including a slot adjacent a lower end thereof. Another aspect of a boat or recreational vehicle ladder apparatus provides a snap-on step tread which can be mounted to a dual-tubular ladder step structure. Another aspect of a boat or recreational vehicle ladder apparatus employs a laterally expandable ladder step which can be retrofit onto an existing ladder. A further aspect employs clasps or hooks to attach and retain a ladder step to generally vertical ladder rails in a tool-free and fastener-free manner.