Working in tenerife for less than 3 months a year then back to uk

[chelseamassive]

I"m considering working at market one day a week to cover my expenses while im here, around 100 to 150 euros a week for up to 3 months,my question is for this amount which would be up to 2,000 euros do i need to declare the amount before i leave,or are you allowed to earn a certain amount before you declare it?Im confused,,what would you do in my situation,thanks for any advice!