Lagoons occupy 13% of the planet's coastal area, provide various ecosystem services, and are among the most threatened ecosystems in the world, mainly due to the intense urbanization of their surroundings. Macroalgae are efficient bioindicators used worldwide for monitoring aquatic environments. In Brazil, studies on macroalgae are concentrated in marine regions. The objective of this work was to conduct a systematic review of studies on marine macroalgae in Brazilian lagoons. Using Google Earth, the lagoons were located and mapped to assess national patterns. Between 09/2021 and 03/2022, searches were conducted in five databases in all languages, using the following keywords: (*alga* OR seaweed) AND (lagoon) AND (Brasil* OR Brazil*). Our results identified about 290 lagoons on the Brazilian coast. The Rio Grande marine ecoregion had the highest number of lagoons (n=125), followed by the northeastern and southeastern ecoregions. Of the 17 coastal states, only four lack lagoons. This systematic review cataloged 36 studies on macroalgae conducted in only 11 lagoons, identifying 216 taxa, with 57% being Rhodophyta, 32% Chlorophyta, and 11% Ochrophyta. Lagoa dos Patos and Araruama had the highest number of studies. The use of these organisms as bioindicators is essential for monitoring the ecological status of these environments. It is recommended that a greater number of lagoons be the focus of long-term monitoring programs such as PELD. The natural conservation of coastal lagoons is important not only for their ecological significance but also for the valuable ecosystem services they provide for human well-being.