There's worry retail investor exuberance in the exchange-traded fund space is flashing a warning signal for markets.

As individuals pour billions of dollars into some of the riskiest pockets of the exchange-traded fund market, some experts like ETF Action's Mike Akins question whether the trend is a sign of markets overheating.

"Product proliferation in the ETF market is at its all-time high right now," the firm's founding partner told CNBC's " ETF Edge " this week. "We are seeing signs of all of those types of niche strategies, especially in the thematic and innovative space, starting to approach 2020, 2021 types of flows again, right at the top of the market."

Institutional investors make up roughly 64% of the overall ETF market, recent 13F filings compiled by ETF Action show. By co

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