This is the 4441st most frequent Russian word.
водных
"Водных" means "of water" or "aquatic" in English.
In this sentence, 'водных' modifies 'организмов', indicating that the organisms are related to or derived from water, highlighting the genitive plural use.
Я изучаю свойства водных организмов.
I study the properties of aquatic organisms.
Here, 'водных' describes 'парках', denoting that the parks are water-based or themed, again in genitive plural form.
Наша экскурсия пройдет в водных парках города.
Our excursion will take place in the water parks of the city.
In this context, 'водных' refers to 'каналов', meaning the canals are associated with water, continuing the descriptive use.