Sango no Umi to Ouji

Collection of series that feature mermaids as characters or as a theme of the series.

OVA's that are not "bonus" or "extra" episodes of a pre existing TV series. Year 2000 edition.

This stack will feature anime with broad ecological and environmentalist themes.

For an anime to be considered environmentalist, it must primarily communicate a message regarding the condition of nature; moreover, it should portray nature as suffering, whether from pollution, deforestation, ecosystem collapse, or similar crises, in a manner that resonates with the Japanese environmentalist movement.

Feel free to recommend another anime I might miss.
Let's start with anime that is not in the database.

From Seitarou Kitayama lost anime: Physiology and Ecology of Plants (Shokubutsu seiri seitai no maki) 1922
source: Promiscuous Media_Film and Visual Culture in Imperial Japan, 1926-1945; pp.160

*Note: For this interest stack, The Anime Encyclopedia has been extensively used.
*Also, gratitude to anime-planet.com for their environmental tag. Without it, a considerable number of anime would be included here.
*Most of the descriptions were co-written using LLM technology, specifically Microsoft Bing Copilot, with the generative prompt: "Hi, can you write me a short synopsis about an anime named ..... with environmentalism themes?"

Update: On 18.8.2024, after watching the third part of the @WooKong1 anime history documentary, I added a few anime titles that were discussed in its ecological section. Overall, I highly recommend the video. A not fully animated movie mention in the video Godzilla vs Hedorah (1971)

OVAs made in the 2000s and beyond that carry on the spirit of the 80s/90s OVA -- a fun, standalone story told in a short amount of time, supported by great production values.