Because oceans occupy most of the earth's surface, it is imperative to extend the Internet of Things (IoT) principles to the existing bodies, paving the way for a new digital trend: the Internet of Underwater Things. Internet of underwater things refers to the worldwide network of smart interconnected underwater objects, which enhances the monitoring of unexplored and vast water areas. It enables various applications like environmental monitoring, disaster prevention, and underground exploration. The Internet of Underground things with such applications is among the leading applied technologies in smart cities. Therefore, this study aims to determine the applications of the Internet of Underwater Things (IoUT) and examine the challenges that lie within designing and implementing such a network. Moreover, the study's significance lies in technology, which determines how effective the implementation of the IoUT would be. The research will use a review of the state of the art to obtain secondary data. The review will then specifically include sustainability, communication networks, and MATLAB & Simulink simulation and analysis related to the IoUT. Based on previous reviews, an optimal network of IoUT enhances the development and integration of various systems for the robust evaluation of water ecosystems. The outcomes include a tested AUV simulation model, which is a crucial part of an IoUT system that can be adjusted to suit local water conditions. The idea of IoUT should be embraced due to its positive impact on social and economic factors.