Final answer:
The correct future form of the verb is 'iremos'.
Step-by-step explanation:
The correct future form of the verb for the sentence 'Todos nosotros vamos al lago' is iremos. This is because 'iremos' is the first person plural form of the verb 'ir' which means 'to go' in English. This verb form is used when expressing future actions. For example, 'Mañana iremos al lago' means 'Tomorrow we will go to the lake'.
Learn more about Verb conjugation in Spanish